1 <?xml version='1.0' encoding='UTF-8'?>
2 <chapter xmlns="http://docbook.org/ns/docbook"
3 xmlns:xl="http://www.w3.org/1999/xlink" version="5.0" xml:lang="en-US"
5 <title xml:id="lustreproc.title">Lustre Parameters</title>
6 <para>There are many parameters for Lustre that can tune client and server
7 performance, change behavior of the system, and report statistics about
8 various subsystems. This chapter describes the various parameters and
9 tunables that are useful for optimizing and monitoring aspects of a Lustre
10 file system. It includes these sections:</para>
13 <para><xref linkend="enabling_interpreting_debugging_logs"/></para>
18 <title>Introduction to Lustre Parameters</title>
19 <para>Lustre parameters and statistics files provide an interface to
20 internal data structures in the kernel that enables monitoring and
21 tuning of many aspects of Lustre file system and application performance.
22 These data structures include settings and metrics for components such
23 as memory, networking, file systems, and kernel housekeeping routines,
24 which are available throughout the hierarchical file layout.
26 <para>Typically, metrics are accessed via <literal>lctl get_param</literal>
27 files and settings are changed by via <literal>lctl set_param</literal>.
28 They allow getting and setting multiple parameters with a single command,
29 through the use of wildcards in one or more part of the parameter name.
30 While each of these parameters maps to files in <literal>/proc</literal>
31 and <literal>/sys</literal> directly, the location of these parameters may
32 change between Lustre releases, so it is recommended to always use
33 <literal>lctl</literal> to access the parameters from userspace scripts.
34 Some data is server-only, some data is client-only, and some data is
35 exported from the client to the server and is thus duplicated in both
38 <para>In the examples in this chapter, <literal>#</literal> indicates
39 a command is entered as root. Lustre servers are named according to the
40 convention <literal><replaceable>fsname</replaceable>-<replaceable>MDT|OSTnumber</replaceable></literal>.
41 The standard UNIX wildcard designation (*) is used to represent any
42 part of a single component of the parameter name, excluding
43 "<literal>.</literal>" and "<literal>/</literal>".
44 It is also possible to use brace <literal>{}</literal>expansion
45 to specify a list of parameter names efficiently.</para>
47 <para>Some examples are shown below:</para>
50 <para> To list available OST targets on a Lustre client:</para>
51 <screen># lctl list_param -F osc.*
52 osc.testfs-OST0000-osc-ffff881071d5cc00/
53 osc.testfs-OST0001-osc-ffff881071d5cc00/
54 osc.testfs-OST0002-osc-ffff881071d5cc00/
55 osc.testfs-OST0003-osc-ffff881071d5cc00/
56 osc.testfs-OST0004-osc-ffff881071d5cc00/
57 osc.testfs-OST0005-osc-ffff881071d5cc00/
58 osc.testfs-OST0006-osc-ffff881071d5cc00/
59 osc.testfs-OST0007-osc-ffff881071d5cc00/
60 osc.testfs-OST0008-osc-ffff881071d5cc00/</screen>
61 <para>In this example, information about OST connections available
62 on a client is displayed (indicated by "osc"). Each of these
63 connections may have numerous sub-parameters as well.</para>
68 <para> To see multiple levels of parameters, use multiple
69 wildcards:<screen># lctl list_param osc.*.*
70 osc.testfs-OST0000-osc-ffff881071d5cc00.active
71 osc.testfs-OST0000-osc-ffff881071d5cc00.blocksize
72 osc.testfs-OST0000-osc-ffff881071d5cc00.checksum_type
73 osc.testfs-OST0000-osc-ffff881071d5cc00.checksums
74 osc.testfs-OST0000-osc-ffff881071d5cc00.connect_flags
75 osc.testfs-OST0000-osc-ffff881071d5cc00.contention_seconds
76 osc.testfs-OST0000-osc-ffff881071d5cc00.cur_dirty_bytes
78 osc.testfs-OST0000-osc-ffff881071d5cc00.rpc_stats</screen></para>
83 <para> To see a specific subset of parameters, use braces, like:
84 <screen># lctl list_param osc.*.{checksum,connect}*
85 osc.testfs-OST0000-osc-ffff881071d5cc00.checksum_type
86 osc.testfs-OST0000-osc-ffff881071d5cc00.checksums
87 osc.testfs-OST0000-osc-ffff881071d5cc00.connect_flags
93 <para> To view a specific file, use <literal>lctl get_param</literal>:
94 <screen># lctl get_param osc.lustre-OST0000*.rpc_stats</screen></para>
97 <para>For more information about using <literal>lctl</literal>, see <xref
98 xmlns:xlink="http://www.w3.org/1999/xlink" linkend="dbdoclet.setting_param_with_lctl"/>.</para>
99 <para>Data can also be viewed using the <literal>cat</literal> command
100 with the full path to the file. The form of the <literal>cat</literal>
101 command is similar to that of the <literal>lctl get_param</literal>
102 command with some differences. Unfortunately, as the Linux kernel has
103 changed over the years, the location of statistics and parameter files
104 has also changed, which means that the Lustre parameter files may be
105 located in either the <literal>/proc</literal> directory, in the
106 <literal>/sys</literal> directory, and/or in the
107 <literal>/sys/kernel/debug</literal> directory, depending on the kernel
108 version and the Lustre version being used. The <literal>lctl</literal>
109 command insulates scripts from these changes and is preferred over direct
110 file access, unless as part of a high-performance monitoring system.
112 <note condition='l2c'><para>Starting in Lustre 2.12, there is
113 <literal>lctl get_param</literal> and <literal>lctl set_param</literal>
114 command can provide <emphasis>tab completion</emphasis> when using an
115 interactive shell with <literal>bash-completion</literal> installed.
116 This simplifies the use of <literal>get_param</literal> significantly,
117 since it provides an interactive list of available parameters.
119 <para>The <literal>llstat</literal> utility can be used to monitor some
120 Lustre file system I/O activity over a specified time period. For more
122 <xref xmlns:xlink="http://www.w3.org/1999/xlink" linkend="dbdoclet.config_llstat"/></para>
123 <para>Some data is imported from attached clients and is available in a
124 directory called <literal>exports</literal> located in the corresponding
125 per-service directory on a Lustre server. For example:
126 <screen>oss:/root# lctl list_param obdfilter.testfs-OST0000.exports.*
127 # hash ldlm_stats stats uuid</screen></para>
129 <title>Identifying Lustre File Systems and Servers</title>
130 <para>Several parameter files on the MGS list existing
131 Lustre file systems and file system servers. The examples below are for
132 a Lustre file system called
133 <literal>testfs</literal> with one MDT and three OSTs.</para>
136 <para> To view all known Lustre file systems, enter:</para>
137 <screen>mgs# lctl get_param mgs.*.filesystems
141 <para> To view the names of the servers in a file system in which least one server is
143 enter:<screen>lctl get_param mgs.*.live.<replaceable><filesystem name></replaceable></screen></para>
144 <para>For example:</para>
145 <screen>mgs# lctl get_param mgs.*.live.testfs
153 Secure RPC Config Rules:
155 imperative_recovery_state:
159 notify_duration_total: 0.001000
160 notify_duation_max: 0.001000
161 notify_count: 4</screen>
164 <para>To list all configured devices on the local node, enter:</para>
165 <screen># lctl device_list
167 1 UP mgc MGC192.168.10.34@tcp 1f45bb57-d9be-2ddb-c0b0-5431a49226705
168 2 UP mdt MDS MDS_uuid 3
169 3 UP lov testfs-mdtlov testfs-mdtlov_UUID 4
170 4 UP mds testfs-MDT0000 testfs-MDT0000_UUID 7
171 5 UP osc testfs-OST0000-osc testfs-mdtlov_UUID 5
172 6 UP osc testfs-OST0001-osc testfs-mdtlov_UUID 5
173 7 UP lov testfs-clilov-ce63ca00 08ac6584-6c4a-3536-2c6d-b36cf9cbdaa04
174 8 UP mdc testfs-MDT0000-mdc-ce63ca00 08ac6584-6c4a-3536-2c6d-b36cf9cbdaa05
175 9 UP osc testfs-OST0000-osc-ce63ca00 08ac6584-6c4a-3536-2c6d-b36cf9cbdaa05
176 10 UP osc testfs-OST0001-osc-ce63ca00 08ac6584-6c4a-3536-2c6d-b36cf9cbdaa05</screen>
177 <para>The information provided on each line includes:</para>
178 <para> - Device number</para>
179 <para> - Device status (UP, INactive, or STopping) </para>
180 <para> - Device name</para>
181 <para> - Device UUID</para>
182 <para> - Reference count (how many users this device has)</para>
185 <para>To display the name of any server, view the device
186 label:<screen>mds# e2label /dev/sda
187 testfs-MDT0000</screen></para>
193 <title>Tuning Multi-Block Allocation (mballoc)</title>
194 <para>Capabilities supported by <literal>mballoc</literal> include:</para>
197 <para> Pre-allocation for single files to help to reduce fragmentation.</para>
200 <para> Pre-allocation for a group of files to enable packing of small files into large,
201 contiguous chunks.</para>
204 <para> Stream allocation to help decrease the seek rate.</para>
207 <para>The following <literal>mballoc</literal> tunables are available:</para>
208 <informaltable frame="all">
210 <colspec colname="c1" colwidth="30*"/>
211 <colspec colname="c2" colwidth="70*"/>
215 <para><emphasis role="bold">Field</emphasis></para>
218 <para><emphasis role="bold">Description</emphasis></para>
226 <literal>mb_max_to_scan</literal></para>
229 <para>Maximum number of free chunks that <literal>mballoc</literal> finds before a
230 final decision to avoid a livelock situation.</para>
236 <literal>mb_min_to_scan</literal></para>
239 <para>Minimum number of free chunks that <literal>mballoc</literal> searches before
240 picking the best chunk for allocation. This is useful for small requests to reduce
241 fragmentation of big free chunks.</para>
247 <literal>mb_order2_req</literal></para>
250 <para>For requests equal to 2^N, where N >= <literal>mb_order2_req</literal>, a
251 fast search is done using a base 2 buddy allocation service.</para>
257 <literal>mb_small_req</literal></para>
260 <para><literal>mb_small_req</literal> - Defines (in MB) the upper bound of "small
262 <para><literal>mb_large_req</literal> - Defines (in MB) the lower bound of "large
264 <para>Requests are handled differently based on size:<itemizedlist>
266 <para>< <literal>mb_small_req</literal> - Requests are packed together to
267 form large, aggregated requests.</para>
270 <para>> <literal>mb_small_req</literal> and < <literal>mb_large_req</literal>
271 - Requests are primarily allocated linearly.</para>
274 <para>> <literal>mb_large_req</literal> - Requests are allocated since hard disk
275 seek time is less of a concern in this case.</para>
277 </itemizedlist></para>
278 <para>In general, small requests are combined to create larger requests, which are
279 then placed close to one another to minimize the number of seeks required to access
286 <literal>mb_large_req</literal></para>
292 <literal>prealloc_table</literal></para>
295 <para>A table of values used to preallocate space when a new request is received. By
296 default, the table looks like
297 this:<screen>prealloc_table
298 4 8 16 32 64 128 256 512 1024 2048 </screen></para>
299 <para>When a new request is received, space is preallocated at the next higher
300 increment specified in the table. For example, for requests of less than 4 file
301 system blocks, 4 blocks of space are preallocated; for requests between 4 and 8, 8
302 blocks are preallocated; and so forth</para>
303 <para>Although customized values can be entered in the table, the performance of
304 general usage file systems will not typically be improved by modifying the table (in
305 fact, in ext4 systems, the table values are fixed). However, for some specialized
306 workloads, tuning the <literal>prealloc_table</literal> values may result in smarter
307 preallocation decisions. </para>
313 <literal>mb_group_prealloc</literal></para>
316 <para>The amount of space (in kilobytes) preallocated for groups of small
323 <para>Buddy group cache information found in
324 <literal>/sys/fs/ldiskfs/<replaceable>disk_device</replaceable>/mb_groups</literal> may
325 be useful for assessing on-disk fragmentation. For
326 example:<screen>cat /proc/fs/ldiskfs/loop0/mb_groups
327 #group: free free frags first pa [ 2^0 2^1 2^2 2^3 2^4 2^5 2^6 2^7 2^8 2^9
329 #0 : 2936 2936 1 42 0 [ 0 0 0 1 1 1 1 2 0 1
330 2 0 0 0 ]</screen></para>
331 <para>In this example, the columns show:<itemizedlist>
333 <para>#group number</para>
336 <para>Available blocks in the group</para>
339 <para>Blocks free on a disk</para>
342 <para>Number of free fragments</para>
345 <para>First free block in the group</para>
348 <para>Number of preallocated chunks (not blocks)</para>
351 <para>A series of available chunks of different sizes</para>
353 </itemizedlist></para>
356 <title>Monitoring Lustre File System I/O</title>
357 <para>A number of system utilities are provided to enable collection of data related to I/O
358 activity in a Lustre file system. In general, the data collected describes:</para>
361 <para> Data transfer rates and throughput of inputs and outputs external to the Lustre file
362 system, such as network requests or disk I/O operations performed</para>
365 <para> Data about the throughput or transfer rates of internal Lustre file system data, such
366 as locks or allocations. </para>
370 <para>It is highly recommended that you complete baseline testing for your Lustre file system
371 to determine normal I/O activity for your hardware, network, and system workloads. Baseline
372 data will allow you to easily determine when performance becomes degraded in your system.
373 Two particularly useful baseline statistics are:</para>
376 <para><literal>brw_stats</literal> – Histogram data characterizing I/O requests to the
377 OSTs. For more details, see <xref xmlns:xlink="http://www.w3.org/1999/xlink"
378 linkend="monitor_ost_block_io_stream"/>.</para>
381 <para><literal>rpc_stats</literal> – Histogram data showing information about RPCs made by
382 clients. For more details, see <xref xmlns:xlink="http://www.w3.org/1999/xlink"
383 linkend="MonitoringClientRCPStream"/>.</para>
387 <section remap="h3" xml:id="MonitoringClientRCPStream">
389 <primary>proc</primary>
390 <secondary>watching RPC</secondary>
391 </indexterm>Monitoring the Client RPC Stream</title>
392 <para>The <literal>rpc_stats</literal> file contains histogram data showing information about
393 remote procedure calls (RPCs) that have been made since this file was last cleared. The
394 histogram data can be cleared by writing any value into the <literal>rpc_stats</literal>
396 <para><emphasis role="italic"><emphasis role="bold">Example:</emphasis></emphasis></para>
397 <screen># lctl get_param osc.testfs-OST0000-osc-ffff810058d2f800.rpc_stats
398 snapshot_time: 1372786692.389858 (secs.usecs)
399 read RPCs in flight: 0
400 write RPCs in flight: 1
401 dio read RPCs in flight: 0
402 dio write RPCs in flight: 0
403 pending write pages: 256
404 pending read pages: 0
407 pages per rpc rpcs % cum % | rpcs % cum %
416 256: 850 100 100 | 18346 99 100
419 rpcs in flight rpcs % cum % | rpcs % cum %
420 0: 691 81 81 | 1740 9 9
421 1: 48 5 86 | 938 5 14
422 2: 29 3 90 | 1059 5 20
423 3: 17 2 92 | 1052 5 26
424 4: 13 1 93 | 920 5 31
425 5: 12 1 95 | 425 2 33
426 6: 10 1 96 | 389 2 35
427 7: 30 3 100 | 11373 61 97
428 8: 0 0 100 | 460 2 100
431 offset rpcs % cum % | rpcs % cum %
432 0: 850 100 100 | 18347 99 99
440 128: 0 0 100 | 4 0 100
443 <para>The header information includes:</para>
446 <para><literal>snapshot_time</literal> - UNIX epoch instant the file was read.</para>
449 <para><literal>read RPCs in flight</literal> - Number of read RPCs issued by the OSC, but
450 not complete at the time of the snapshot. This value should always be less than or equal
451 to <literal>max_rpcs_in_flight</literal>.</para>
454 <para><literal>write RPCs in flight</literal> - Number of write RPCs issued by the OSC,
455 but not complete at the time of the snapshot. This value should always be less than or
456 equal to <literal>max_rpcs_in_flight</literal>.</para>
459 <para><literal>dio read RPCs in flight</literal> - Direct I/O (as opposed to block I/O)
460 read RPCs issued but not completed at the time of the snapshot.</para>
463 <para><literal>dio write RPCs in flight</literal> - Direct I/O (as opposed to block I/O)
464 write RPCs issued but not completed at the time of the snapshot.</para>
467 <para><literal>pending write pages</literal> - Number of pending write pages that have
468 been queued for I/O in the OSC.</para>
471 <para><literal>pending read pages</literal> - Number of pending read pages that have been
472 queued for I/O in the OSC.</para>
475 <para>The tabular data is described in the table below. Each row in the table shows the number
476 of reads or writes (<literal>ios</literal>) occurring for the statistic, the relative
477 percentage (<literal>%</literal>) of total reads or writes, and the cumulative percentage
478 (<literal>cum %</literal>) to that point in the table for the statistic.</para>
479 <informaltable frame="all">
481 <colspec colname="c1" colwidth="40*"/>
482 <colspec colname="c2" colwidth="60*"/>
486 <para><emphasis role="bold">Field</emphasis></para>
489 <para><emphasis role="bold">Description</emphasis></para>
496 <para> pages per RPC</para>
499 <para>Shows cumulative RPC reads and writes organized according to the number of
500 pages in the RPC. A single page RPC increments the <literal>0:</literal>
506 <para> RPCs in flight</para>
509 <para> Shows the number of RPCs that are pending when an RPC is sent. When the first
510 RPC is sent, the <literal>0:</literal> row is incremented. If the first RPC is
511 sent while another RPC is pending, the <literal>1:</literal> row is incremented
520 <para> The page index of the first page read from or written to the object by the
527 <para><emphasis role="italic"><emphasis role="bold">Analysis:</emphasis></emphasis></para>
528 <para>This table provides a way to visualize the concurrency of the RPC stream. Ideally, you
529 will see a large clump around the <literal>max_rpcs_in_flight value</literal>, which shows
530 that the network is being kept busy.</para>
531 <para>For information about optimizing the client I/O RPC stream, see <xref
532 xmlns:xlink="http://www.w3.org/1999/xlink" linkend="TuningClientIORPCStream"/>.</para>
534 <section xml:id="lustreproc.clientstats" remap="h3">
536 <primary>proc</primary>
537 <secondary>client stats</secondary>
538 </indexterm>Monitoring Client Activity</title>
539 <para>The <literal>stats</literal> file maintains statistics accumulate during typical
540 operation of a client across the VFS interface of the Lustre file system. Only non-zero
541 parameters are displayed in the file. </para>
542 <para>Client statistics are enabled by default.</para>
544 <para>Statistics for all mounted file systems can be discovered by
545 entering:<screen>lctl get_param llite.*.stats</screen></para>
547 <para><emphasis role="italic"><emphasis role="bold">Example:</emphasis></emphasis></para>
548 <screen>client# lctl get_param llite.*.stats
549 snapshot_time 1308343279.169704 secs.usecs
550 dirty_pages_hits 14819716 samples [regs]
551 dirty_pages_misses 81473472 samples [regs]
552 read_bytes 36502963 samples [bytes] 1 26843582 55488794
553 write_bytes 22985001 samples [bytes] 0 125912 3379002
554 brw_read 2279 samples [pages] 1 1 2270
555 ioctl 186749 samples [regs]
556 open 3304805 samples [regs]
557 close 3331323 samples [regs]
558 seek 48222475 samples [regs]
559 fsync 963 samples [regs]
560 truncate 9073 samples [regs]
561 setxattr 19059 samples [regs]
562 getxattr 61169 samples [regs]
564 <para> The statistics can be cleared by echoing an empty string into the
565 <literal>stats</literal> file or by using the command:
566 <screen>lctl set_param llite.*.stats=0</screen></para>
567 <para>The statistics displayed are described in the table below.</para>
568 <informaltable frame="all">
570 <colspec colname="c1" colwidth="3*"/>
571 <colspec colname="c2" colwidth="7*"/>
575 <para><emphasis role="bold">Entry</emphasis></para>
578 <para><emphasis role="bold">Description</emphasis></para>
586 <literal>snapshot_time</literal></para>
589 <para>UNIX epoch instant the stats file was read.</para>
595 <literal>dirty_page_hits</literal></para>
598 <para>The number of write operations that have been satisfied by the dirty page
599 cache. See <xref xmlns:xlink="http://www.w3.org/1999/xlink"
600 linkend="TuningClientIORPCStream"/> for more information about dirty cache
601 behavior in a Lustre file system.</para>
607 <literal>dirty_page_misses</literal></para>
610 <para>The number of write operations that were not satisfied by the dirty page
617 <literal>read_bytes</literal></para>
620 <para>The number of read operations that have occurred. Three additional parameters
621 are displayed:</para>
626 <para>The minimum number of bytes read in a single request since the counter
633 <para>The maximum number of bytes read in a single request since the counter
640 <para>The accumulated sum of bytes of all read requests since the counter was
650 <literal>write_bytes</literal></para>
653 <para>The number of write operations that have occurred. Three additional parameters
654 are displayed:</para>
659 <para>The minimum number of bytes written in a single request since the
660 counter was reset.</para>
666 <para>The maximum number of bytes written in a single request since the
667 counter was reset.</para>
673 <para>The accumulated sum of bytes of all write requests since the counter was
683 <literal>brw_read</literal></para>
686 <para>The number of pages that have been read. Three additional parameters are
692 <para>The minimum number of bytes read in a single block read/write
693 (<literal>brw</literal>) read request since the counter was reset.</para>
699 <para>The maximum number of bytes read in a single <literal>brw</literal> read
700 requests since the counter was reset.</para>
706 <para>The accumulated sum of bytes of all <literal>brw</literal> read requests
707 since the counter was reset.</para>
716 <literal>ioctl</literal></para>
719 <para>The number of combined file and directory <literal>ioctl</literal>
726 <literal>open</literal></para>
729 <para>The number of open operations that have succeeded.</para>
735 <literal>close</literal></para>
738 <para>The number of close operations that have succeeded.</para>
744 <literal>seek</literal></para>
747 <para>The number of times <literal>seek</literal> has been called.</para>
753 <literal>fsync</literal></para>
756 <para>The number of times <literal>fsync</literal> has been called.</para>
762 <literal>truncate</literal></para>
765 <para>The total number of calls to both locked and lockless
766 <literal>truncate</literal>.</para>
772 <literal>setxattr</literal></para>
775 <para>The number of times extended attributes have been set. </para>
781 <literal>getxattr</literal></para>
784 <para>The number of times value(s) of extended attributes have been fetched.</para>
790 <para><emphasis role="italic"><emphasis role="bold">Analysis:</emphasis></emphasis></para>
791 <para>Information is provided about the amount and type of I/O activity is taking place on the
796 <primary>proc</primary>
797 <secondary>read/write survey</secondary>
798 </indexterm>Monitoring Client Read-Write Offset Statistics</title>
799 <para>When the <literal>offset_stats</literal> parameter is set, statistics are maintained for
800 occurrences of a series of read or write calls from a process that did not access the next
801 sequential location. The <literal>OFFSET</literal> field is reset to 0 (zero) whenever a
802 different file is read or written.</para>
804 <para>By default, statistics are not collected in the <literal>offset_stats</literal>,
805 <literal>extents_stats</literal>, and <literal>extents_stats_per_process</literal> files
806 to reduce monitoring overhead when this information is not needed. The collection of
807 statistics in all three of these files is activated by writing
808 anything, except for 0 (zero) and "disable", into any one of the
811 <para><emphasis role="italic"><emphasis role="bold">Example:</emphasis></emphasis></para>
812 <screen># lctl get_param llite.testfs-f57dee0.offset_stats
813 snapshot_time: 1155748884.591028 (secs.usecs)
814 RANGE RANGE SMALLEST LARGEST
815 R/W PID START END EXTENT EXTENT OFFSET
816 R 8385 0 128 128 128 0
817 R 8385 0 224 224 224 -128
818 W 8385 0 250 50 100 0
819 W 8385 100 1110 10 500 -150
820 W 8384 0 5233 5233 5233 0
821 R 8385 500 600 100 100 -610</screen>
822 <para>In this example, <literal>snapshot_time</literal> is the UNIX epoch instant the file was
823 read. The tabular data is described in the table below.</para>
824 <para>The <literal>offset_stats</literal> file can be cleared by
825 entering:<screen>lctl set_param llite.*.offset_stats=0</screen></para>
826 <informaltable frame="all">
828 <colspec colname="c1" colwidth="50*"/>
829 <colspec colname="c2" colwidth="50*"/>
833 <para><emphasis role="bold">Field</emphasis></para>
836 <para><emphasis role="bold">Description</emphasis></para>
846 <para>Indicates if the non-sequential call was a read or write</para>
854 <para>Process ID of the process that made the read/write call.</para>
859 <para>RANGE START/RANGE END</para>
862 <para>Range in which the read/write calls were sequential.</para>
867 <para>SMALLEST EXTENT </para>
870 <para>Smallest single read/write in the corresponding range (in bytes).</para>
875 <para>LARGEST EXTENT </para>
878 <para>Largest single read/write in the corresponding range (in bytes).</para>
886 <para>Difference between the previous range end and the current range start.</para>
892 <para><emphasis role="italic"><emphasis role="bold">Analysis:</emphasis></emphasis></para>
893 <para>This data provides an indication of how contiguous or fragmented the data is. For
894 example, the fourth entry in the example above shows the writes for this RPC were sequential
895 in the range 100 to 1110 with the minimum write 10 bytes and the maximum write 500 bytes.
896 The range started with an offset of -150 from the <literal>RANGE END</literal> of the
897 previous entry in the example.</para>
901 <primary>proc</primary>
902 <secondary>read/write survey</secondary>
903 </indexterm>Monitoring Client Read-Write Extent Statistics</title>
904 <para>For in-depth troubleshooting, client read-write extent statistics can be accessed to
905 obtain more detail about read/write I/O extents for the file system or for a particular
908 <para>By default, statistics are not collected in the <literal>offset_stats</literal>,
909 <literal>extents_stats</literal>, and <literal>extents_stats_per_process</literal> files
910 to reduce monitoring overhead when this information is not needed. The collection of
911 statistics in all three of these files is activated by writing
912 anything, except for 0 (zero) and "disable", into any one of the
916 <title>Client-Based I/O Extent Size Survey</title>
917 <para>The <literal>extents_stats</literal> histogram in the
918 <literal>llite</literal> directory shows the statistics for the sizes
919 of the read/write I/O extents. This file does not maintain the per
920 process statistics.</para>
921 <para><emphasis role="italic"><emphasis role="bold">Example:</emphasis></emphasis></para>
922 <screen># lctl get_param llite.testfs-*.extents_stats
923 snapshot_time: 1213828728.348516 (secs.usecs)
925 extents calls % cum% | calls % cum%
927 0K - 4K : 0 0 0 | 2 2 2
928 4K - 8K : 0 0 0 | 0 0 2
929 8K - 16K : 0 0 0 | 0 0 2
930 16K - 32K : 0 0 0 | 20 23 26
931 32K - 64K : 0 0 0 | 0 0 26
932 64K - 128K : 0 0 0 | 51 60 86
933 128K - 256K : 0 0 0 | 0 0 86
934 256K - 512K : 0 0 0 | 0 0 86
935 512K - 1024K : 0 0 0 | 0 0 86
936 1M - 2M : 0 0 0 | 11 13 100</screen>
937 <para>In this example, <literal>snapshot_time</literal> is the UNIX epoch instant the file
938 was read. The table shows cumulative extents organized according to size with statistics
939 provided separately for reads and writes. Each row in the table shows the number of RPCs
940 for reads and writes respectively (<literal>calls</literal>), the relative percentage of
941 total calls (<literal>%</literal>), and the cumulative percentage to
942 that point in the table of calls (<literal>cum %</literal>). </para>
943 <para> The file can be cleared by issuing the following command:
944 <screen># lctl set_param llite.testfs-*.extents_stats=1</screen></para>
947 <title>Per-Process Client I/O Statistics</title>
948 <para>The <literal>extents_stats_per_process</literal> file maintains the I/O extent size
949 statistics on a per-process basis.</para>
950 <para><emphasis role="italic"><emphasis role="bold">Example:</emphasis></emphasis></para>
951 <screen># lctl get_param llite.testfs-*.extents_stats_per_process
952 snapshot_time: 1213828762.204440 (secs.usecs)
954 extents calls % cum% | calls % cum%
957 0K - 4K : 0 0 0 | 0 0 0
958 4K - 8K : 0 0 0 | 0 0 0
959 8K - 16K : 0 0 0 | 0 0 0
960 16K - 32K : 0 0 0 | 0 0 0
961 32K - 64K : 0 0 0 | 0 0 0
962 64K - 128K : 0 0 0 | 0 0 0
963 128K - 256K : 0 0 0 | 0 0 0
964 256K - 512K : 0 0 0 | 0 0 0
965 512K - 1024K : 0 0 0 | 0 0 0
966 1M - 2M : 0 0 0 | 10 100 100
969 0K - 4K : 0 0 0 | 0 0 0
970 4K - 8K : 0 0 0 | 0 0 0
971 8K - 16K : 0 0 0 | 0 0 0
972 16K - 32K : 0 0 0 | 20 100 100
975 0K - 4K : 0 0 0 | 0 0 0
976 4K - 8K : 0 0 0 | 0 0 0
977 8K - 16K : 0 0 0 | 0 0 0
978 16K - 32K : 0 0 0 | 0 0 0
979 32K - 64K : 0 0 0 | 0 0 0
980 64K - 128K : 0 0 0 | 16 100 100
983 0K - 4K : 0 0 0 | 1 100 100
986 0K - 4K : 0 0 0 | 1 100 100
989 <para>This table shows cumulative extents organized according to size for each process ID
990 (PID) with statistics provided separately for reads and writes. Each row in the table
991 shows the number of RPCs for reads and writes respectively (<literal>calls</literal>), the
992 relative percentage of total calls (<literal>%</literal>), and the cumulative percentage
993 to that point in the table of calls (<literal>cum %</literal>). </para>
996 <section xml:id="monitor_ost_block_io_stream">
998 <primary>proc</primary>
999 <secondary>block I/O</secondary>
1000 </indexterm>Monitoring the OST Block I/O Stream</title>
1001 <para>The <literal>brw_stats</literal> parameter file below the
1002 <literal>osd-ldiskfs</literal> or <literal>osd-zfs</literal> directory
1003 contains histogram data showing statistics for number of I/O requests
1004 sent to the disk, their size, and whether they are contiguous on the
1006 <para><emphasis role="italic"><emphasis role="bold">Example:</emphasis></emphasis></para>
1007 <para>Enter on the OSS or MDS:</para>
1008 <screen>oss# lctl get_param osd-*.*.brw_stats
1009 snapshot_time: 1372775039.769045 (secs.usecs)
1011 pages per bulk r/w rpcs % cum % | rpcs % cum %
1012 1: 108 100 100 | 39 0 0
1017 32: 0 0 100 | 17 0 0
1018 64: 0 0 100 | 12 0 0
1019 128: 0 0 100 | 24 0 0
1020 256: 0 0 100 | 23142 99 100
1023 discontiguous pages rpcs % cum % | rpcs % cum %
1024 0: 108 100 100 | 23245 100 100
1027 discontiguous blocks rpcs % cum % | rpcs % cum %
1028 0: 108 100 100 | 23243 99 99
1029 1: 0 0 100 | 2 0 100
1032 disk fragmented I/Os ios % cum % | ios % cum %
1034 1: 14 12 100 | 23243 99 99
1035 2: 0 0 100 | 2 0 100
1038 disk I/Os in flight ios % cum % | ios % cum %
1039 1: 14 100 100 | 20896 89 89
1040 2: 0 0 100 | 1071 4 94
1041 3: 0 0 100 | 573 2 96
1042 4: 0 0 100 | 300 1 98
1043 5: 0 0 100 | 166 0 98
1044 6: 0 0 100 | 108 0 99
1045 7: 0 0 100 | 81 0 99
1046 8: 0 0 100 | 47 0 99
1047 9: 0 0 100 | 5 0 100
1050 I/O time (1/1000s) ios % cum % | ios % cum %
1053 4: 14 12 100 | 27 0 0
1055 16: 0 0 100 | 31 0 0
1056 32: 0 0 100 | 38 0 0
1057 64: 0 0 100 | 18979 81 82
1058 128: 0 0 100 | 943 4 86
1059 256: 0 0 100 | 1233 5 91
1060 512: 0 0 100 | 1825 7 99
1061 1K: 0 0 100 | 99 0 99
1062 2K: 0 0 100 | 0 0 99
1063 4K: 0 0 100 | 0 0 99
1064 8K: 0 0 100 | 49 0 100
1067 disk I/O size ios % cum % | ios % cum %
1068 4K: 14 100 100 | 41 0 0
1070 16K: 0 0 100 | 1 0 0
1071 32K: 0 0 100 | 0 0 0
1072 64K: 0 0 100 | 4 0 0
1073 128K: 0 0 100 | 17 0 0
1074 256K: 0 0 100 | 12 0 0
1075 512K: 0 0 100 | 24 0 0
1076 1M: 0 0 100 | 23142 99 100
1078 <para>The tabular data is described in the table below. Each row in the
1079 table shows the number of reads and writes occurring for the statistic
1080 (<literal>ios</literal>), the relative percentage of total reads or
1081 writes (<literal>%</literal>), and the cumulative percentage to that
1082 point in the table for the statistic (<literal>cum %</literal>). </para>
1083 <informaltable frame="all">
1085 <colspec colname="c1" colwidth="40*"/>
1086 <colspec colname="c2" colwidth="60*"/>
1090 <para><emphasis role="bold">Field</emphasis></para>
1093 <para><emphasis role="bold">Description</emphasis></para>
1101 <literal>pages per bulk r/w</literal></para>
1104 <para>Number of pages per RPC request, which should match aggregate client
1105 <literal>rpc_stats</literal> (see <xref
1106 xmlns:xlink="http://www.w3.org/1999/xlink" linkend="MonitoringClientRCPStream"
1113 <literal>discontiguous pages</literal></para>
1116 <para>Number of discontinuities in the logical file offset of each page in a single
1123 <literal>discontiguous blocks</literal></para>
1126 <para>Number of discontinuities in the physical block allocation in the file system
1127 for a single RPC.</para>
1132 <para><literal>disk fragmented I/Os</literal></para>
1135 <para>Number of I/Os that were not written entirely sequentially.</para>
1140 <para><literal>disk I/Os in flight</literal></para>
1143 <para>Number of disk I/Os currently pending.</para>
1148 <para><literal>I/O time (1/1000s)</literal></para>
1151 <para>Amount of time for each I/O operation to complete.</para>
1156 <para><literal>disk I/O size</literal></para>
1159 <para>Size of each I/O operation.</para>
1165 <para><emphasis role="italic"><emphasis role="bold">Analysis:</emphasis></emphasis></para>
1166 <para>This data provides an indication of extent size and distribution in the file
1171 <title>Tuning Lustre File System I/O</title>
1172 <para>Each OSC has its own tree of tunables. For example:</para>
1173 <screen>$ lctl lctl list_param osc.*.*
1174 osc.myth-OST0000-osc-ffff8804296c2800.active
1175 osc.myth-OST0000-osc-ffff8804296c2800.blocksize
1176 osc.myth-OST0000-osc-ffff8804296c2800.checksum_dump
1177 osc.myth-OST0000-osc-ffff8804296c2800.checksum_type
1178 osc.myth-OST0000-osc-ffff8804296c2800.checksums
1179 osc.myth-OST0000-osc-ffff8804296c2800.connect_flags
1182 osc.myth-OST0000-osc-ffff8804296c2800.state
1183 osc.myth-OST0000-osc-ffff8804296c2800.stats
1184 osc.myth-OST0000-osc-ffff8804296c2800.timeouts
1185 osc.myth-OST0000-osc-ffff8804296c2800.unstable_stats
1186 osc.myth-OST0000-osc-ffff8804296c2800.uuid
1187 osc.myth-OST0001-osc-ffff8804296c2800.active
1188 osc.myth-OST0001-osc-ffff8804296c2800.blocksize
1189 osc.myth-OST0001-osc-ffff8804296c2800.checksum_dump
1190 osc.myth-OST0001-osc-ffff8804296c2800.checksum_type
1194 <para>The following sections describe some of the parameters that can
1195 be tuned in a Lustre file system.</para>
1196 <section remap="h3" xml:id="TuningClientIORPCStream">
1198 <primary>proc</primary>
1199 <secondary>RPC tunables</secondary>
1200 </indexterm>Tuning the Client I/O RPC Stream</title>
1201 <para>Ideally, an optimal amount of data is packed into each I/O RPC
1202 and a consistent number of issued RPCs are in progress at any time.
1203 To help optimize the client I/O RPC stream, several tuning variables
1204 are provided to adjust behavior according to network conditions and
1205 cluster size. For information about monitoring the client I/O RPC
1207 xmlns:xlink="http://www.w3.org/1999/xlink" linkend="MonitoringClientRCPStream"/>.</para>
1208 <para>RPC stream tunables include:</para>
1212 <para><literal>osc.<replaceable>osc_instance</replaceable>.checksums</literal>
1213 - Controls whether the client will calculate data integrity
1214 checksums for the bulk data transferred to the OST. Data
1215 integrity checksums are enabled by default. The algorithm used
1216 can be set using the <literal>checksum_type</literal> parameter.
1220 <para><literal>osc.<replaceable>osc_instance</replaceable>.checksum_type</literal>
1221 - Controls the data integrity checksum algorithm used by the
1222 client. The available algorithms are determined by the set of
1223 algorihtms. The checksum algorithm used by default is determined
1224 by first selecting the fastest algorithms available on the OST,
1225 and then selecting the fastest of those algorithms on the client,
1226 which depends on available optimizations in the CPU hardware and
1227 kernel. The default algorithm can be overridden by writing the
1228 algorithm name into the <literal>checksum_type</literal>
1229 parameter. Available checksum types can be seen on the client by
1230 reading the <literal>checksum_type</literal> parameter. Currently
1231 supported checksum types are:
1232 <literal>adler</literal>,
1233 <literal>crc32</literal>,
1234 <literal>crc32c</literal>
1236 <para condition="l2C">
1237 In Lustre release 2.12 additional checksum types were added to
1238 allow end-to-end checksum integration with T10-PI capable
1239 hardware. The client will compute the appropriate checksum
1240 type, based on the checksum type used by the storage, for the
1241 RPC checksum, which will be verified by the server and passed
1242 on to the storage. The T10-PI checksum types are:
1243 <literal>t10ip512</literal>,
1244 <literal>t10ip4K</literal>,
1245 <literal>t10crc512</literal>,
1246 <literal>t10crc4K</literal>
1250 <para><literal>osc.<replaceable>osc_instance</replaceable>.max_dirty_mb</literal>
1251 - Controls how many MiB of dirty data can be written into the
1252 client pagecache for writes by <emphasis>each</emphasis> OSC.
1253 When this limit is reached, additional writes block until
1254 previously-cached data is written to the server. This may be
1255 changed by the <literal>lctl set_param</literal> command. Only
1256 values larger than 0 and smaller than the lesser of 2048 MiB or
1257 1/4 of client RAM are valid. Performance can suffers if the
1258 client cannot aggregate enough data per OSC to form a full RPC
1259 (as set by the <literal>max_pages_per_rpc</literal>) parameter,
1260 unless the application is doing very large writes itself.
1262 <para>To maximize performance, the value for
1263 <literal>max_dirty_mb</literal> is recommended to be at least
1264 4 * <literal>max_pages_per_rpc</literal> *
1265 <literal>max_rpcs_in_flight</literal>.
1269 <para><literal>osc.<replaceable>osc_instance</replaceable>.cur_dirty_bytes</literal>
1270 - A read-only value that returns the current number of bytes
1271 written and cached by this OSC.
1275 <para><literal>osc.<replaceable>osc_instance</replaceable>.max_pages_per_rpc</literal>
1276 - The maximum number of pages that will be sent in a single RPC
1277 request to the OST. The minimum value is one page and the maximum
1278 value is 16 MiB (4096 on systems with <literal>PAGE_SIZE</literal>
1279 of 4 KiB), with the default value of 4 MiB in one RPC. The upper
1280 limit may also be constrained by <literal>ofd.*.brw_size</literal>
1281 setting on the OSS, and applies to all clients connected to that
1282 OST. It is also possible to specify a units suffix (e.g.
1283 <literal>max_pages_per_rpc=4M</literal>), so the RPC size can be
1284 set independently of the client <literal>PAGE_SIZE</literal>.
1288 <para><literal>osc.<replaceable>osc_instance</replaceable>.max_rpcs_in_flight</literal>
1289 - The maximum number of concurrent RPCs in flight from an OSC to
1290 its OST. If the OSC tries to initiate an RPC but finds that it
1291 already has the same number of RPCs outstanding, it will wait to
1292 issue further RPCs until some complete. The minimum setting is 1
1293 and maximum setting is 256. The default value is 8 RPCs.
1295 <para>To improve small file I/O performance, increase the
1296 <literal>max_rpcs_in_flight</literal> value.
1300 <para><literal>llite.<replaceable>fsname_instance</replaceable>.max_cached_mb</literal>
1301 - Maximum amount of read+write data cached by the client. The
1302 default value is 1/2 of the client RAM.
1308 <para>The value for <literal><replaceable>osc_instance</replaceable></literal>
1309 and <literal><replaceable>fsname_instance</replaceable></literal>
1310 are unique to each mount point to allow associating osc, mdc, lov,
1311 lmv, and llite parameters with the same mount point. However, it is
1312 common for scripts to use a wildcard <literal>*</literal> or a
1313 filesystem-specific wildcard
1314 <literal><replaceable>fsname-*</replaceable></literal> to specify
1315 the parameter settings uniformly on all clients. For example:
1317 client$ lctl get_param osc.testfs-OST0000*.rpc_stats
1318 osc.testfs-OST0000-osc-ffff88107412f400.rpc_stats=
1319 snapshot_time: 1375743284.337839 (secs.usecs)
1320 read RPCs in flight: 0
1321 write RPCs in flight: 0
1325 <section remap="h3" xml:id="TuningClientReadahead">
1327 <primary>proc</primary>
1328 <secondary>readahead</secondary>
1329 </indexterm>Tuning File Readahead and Directory Statahead</title>
1330 <para>File readahead and directory statahead enable reading of data
1331 into memory before a process requests the data. File readahead prefetches
1332 file content data into memory for <literal>read()</literal> related
1333 calls, while directory statahead fetches file metadata into memory for
1334 <literal>readdir()</literal> and <literal>stat()</literal> related
1335 calls. When readahead and statahead work well, a process that accesses
1336 data finds that the information it needs is available immediately in
1337 memory on the client when requested without the delay of network I/O.
1339 <section remap="h4">
1340 <title>Tuning File Readahead</title>
1341 <para>File readahead is triggered when two or more sequential reads
1342 by an application fail to be satisfied by data in the Linux buffer
1343 cache. The size of the initial readahead is determined by the RPC
1344 size and the file stripe size, but will typically be at least 1 MiB.
1345 Additional readaheads grow linearly and increment until the per-file
1346 or per-system readahead cache limit on the client is reached.</para>
1347 <para>Readahead tunables include:</para>
1350 <para><literal>llite.<replaceable>fsname_instance</replaceable>.max_read_ahead_mb</literal>
1351 - Controls the maximum amount of data readahead on all files.
1352 Files are read ahead in RPC-sized chunks (4 MiB, or the size of
1353 the <literal>read()</literal> call, if larger) after the second
1354 sequential read on a file descriptor. Random reads are done at
1355 the size of the <literal>read()</literal> call only (no
1356 readahead). Reads to non-contiguous regions of the file reset
1357 the readahead algorithm, and readahead is not triggered until
1358 sequential reads take place again.
1361 This is the global limit for all files and cannot be larger than
1362 1/2 of the client RAM. To disable readahead, set
1363 <literal>max_read_ahead_mb=0</literal>.
1367 <para><literal>llite.<replaceable>fsname_instance</replaceable>.max_read_ahead_per_file_mb</literal>
1368 - Controls the maximum number of megabytes (MiB) of data that
1369 should be prefetched by the client when sequential reads are
1370 detected on one file. This is the per-file readahead limit and
1371 cannot be larger than <literal>max_read_ahead_mb</literal>.
1375 <para><literal>llite.<replaceable>fsname_instance</replaceable>.max_read_ahead_whole_mb</literal>
1376 - Controls the maximum size of a file in MiB that is read in its
1377 entirety upon access, regardless of the size of the
1378 <literal>read()</literal> call. This avoids multiple small read
1379 RPCs on relatively small files, when it is not possible to
1380 efficiently detect a sequential read pattern before the whole
1383 <para>The default value is the greater of 2 MiB or the size of one
1384 RPC, as given by <literal>max_pages_per_rpc</literal>.
1390 <title>Tuning Directory Statahead and AGL</title>
1391 <para>Many system commands, such as <literal>ls –l</literal>,
1392 <literal>du</literal>, and <literal>find</literal>, traverse a
1393 directory sequentially. To make these commands run efficiently, the
1394 directory statahead can be enabled to improve the performance of
1395 directory traversal.</para>
1396 <para>The statahead tunables are:</para>
1399 <para><literal>statahead_max</literal> -
1400 Controls the maximum number of file attributes that will be
1401 prefetched by the statahead thread. By default, statahead is
1402 enabled and <literal>statahead_max</literal> is 32 files.</para>
1403 <para>To disable statahead, set <literal>statahead_max</literal>
1404 to zero via the following command on the client:</para>
1405 <screen>lctl set_param llite.*.statahead_max=0</screen>
1406 <para>To change the maximum statahead window size on a client:</para>
1407 <screen>lctl set_param llite.*.statahead_max=<replaceable>n</replaceable></screen>
1408 <para>The maximum <literal>statahead_max</literal> is 8192 files.
1410 <para>The directory statahead thread will also prefetch the file
1411 size/block attributes from the OSTs, so that all file attributes
1412 are available on the client when requested by an application.
1413 This is controlled by the asynchronous glimpse lock (AGL) setting.
1414 The AGL behaviour can be disabled by setting:</para>
1415 <screen>lctl set_param llite.*.statahead_agl=0</screen>
1418 <para><literal>statahead_stats</literal> -
1419 A read-only interface that provides current statahead and AGL
1420 statistics, such as how many times statahead/AGL has been triggered
1421 since the last mount, how many statahead/AGL failures have occurred
1422 due to an incorrect prediction or other causes.</para>
1424 <para>AGL behaviour is affected by statahead since the inodes
1425 processed by AGL are built by the statahead thread. If
1426 statahead is disabled, then AGL is also disabled.</para>
1432 <section remap="h3">
1434 <primary>proc</primary>
1435 <secondary>read cache</secondary>
1436 </indexterm>Tuning Server Read Cache</title>
1437 <para>The server read cache feature provides read-only caching of file
1438 data on an OSS or MDS (for Data-on-MDT). This functionality uses the
1439 Linux page cache to store the data and uses as much physical memory
1440 as is allocated.</para>
1441 <para>The server read cache can improves Lustre file system performance
1442 in these situations:</para>
1445 <para>Many clients are accessing the same data set (as in HPC
1446 applications or when diskless clients boot from the Lustre file
1450 <para>One client is writing data while another client is reading
1451 it (i.e., clients are exchanging data via the filesystem).</para>
1454 <para>A client has very limited caching of its own.</para>
1457 <para>The server read cache offers these benefits:</para>
1460 <para>Allows servers to cache read data more frequently.</para>
1463 <para>Improves repeated reads to match network speeds instead of
1464 storage speeds.</para>
1467 <para>Provides the building blocks for server write cache
1468 (small-write aggregation).</para>
1471 <section remap="h4">
1472 <title>Using Server Read Cache</title>
1473 <para>The server read cache is implemented on the OSS and MDS, and does
1474 not require any special support on the client side. Since the server
1475 read cache uses the memory available in the Linux page cache, the
1476 appropriate amount of memory for the cache should be determined based
1477 on I/O patterns. If the data is mostly reads, then more cache is
1478 beneficial on the server than would be needed for mostly writes.
1480 <para>The server read cache is managed using the following tunables.
1481 Many tunables are available for both <literal>osd-ldiskfs</literal>
1482 and <literal>osd-zfs</literal>, but in some cases the implementation
1483 of <literal>osd-zfs</literal> prevents their use.</para>
1486 <para><literal>read_cache_enable</literal> - High-level control of
1487 whether data read from storage during a read request is kept in
1488 memory and available for later read requests for the same data,
1489 without having to re-read it from storage. By default, read cache
1490 is enabled (<literal>read_cache_enable=1</literal>) for HDD OSDs
1491 and automatically disabled for flash OSDs
1492 (<literal>nonrotational=1</literal>).
1493 The read cache cannot be disabled for <literal>osd-zfs</literal>,
1494 and as a result this parameter is unavailable for that backend.
1496 <para>When the server receives a read request from a client,
1497 it reads data from storage into its memory and sends the data
1498 to the client. If read cache is enabled for the target,
1499 and the RPC and object size also meet the other criterion below,
1500 this data may stay in memory after the client request has
1501 completed. If later read requests for the same data are received,
1502 if the data is still in cache the server skips reading it from
1503 storage. The cache is managed by the Linux kernel globally
1504 across all targets on that server so that the infrequently used
1505 cache pages are dropped from memory when the free memory is
1507 <para>If read cache is disabled
1508 (<literal>read_cache_enable=0</literal>), or the read or object
1509 is large enough that it will not benefit from caching, the server
1510 discards the data after the read request from the client is
1511 completed. For subsequent read requests the server again reads
1512 the data from storage.</para>
1513 <para>To disable read cache on all targets of a server, run:</para>
1515 oss1# lctl set_param osd-*.*.read_cache_enable=0
1517 <para>To re-enable read cache on one target, run:</para>
1519 oss1# lctl set_param osd-*.{target_name}.read_cache_enable=1
1521 <para>To check if read cache is enabled on targets on a server, run:
1524 oss1# lctl get_param osd-*.*.read_cache_enable
1528 <para><literal>writethrough_cache_enable</literal> - High-level
1529 control of whether data sent to the server as a write request is
1530 kept in the read cache and available for later reads, or if it is
1531 discarded when the write completes. By default, writethrough
1532 cache is enabled (<literal>writethrough_cache_enable=1</literal>)
1533 for HDD OSDs and automatically disabled for flash OSDs
1534 (<literal>nonrotational=1</literal>).
1535 The write cache cannot be disabled for <literal>osd-zfs</literal>,
1536 and as a result this parameter is unavailable for that backend.
1538 <para>When the server receives write requests from a client, it
1539 fetches data from the client into its memory and writes the data
1540 to storage. If the writethrough cache is enabled for the target,
1541 and the RPC and object size meet the other criterion below,
1542 this data may stay in memory after the write request has
1543 completed. If later read or partial-block write requests for this
1544 same data are received, if the data is still in cache the server
1545 skips reading it from storage.
1547 <para>If the writethrough cache is disabled
1548 (<literal>writethrough_cache_enabled=0</literal>), or the
1549 write or object is large enough that it will not benefit from
1550 caching, the server discards the data after the write request
1551 from the client is completed. For subsequent read requests, or
1552 partial-page write requests, the server must re-read the data
1553 from storage.</para>
1554 <para>Enabling writethrough cache is advisable if clients are doing
1555 small or unaligned writes that would cause partial-page updates,
1556 or if the files written by one node are immediately being read by
1557 other nodes. Some examples where enabling writethrough cache
1558 might be useful include producer-consumer I/O models or
1559 shared-file writes that are not aligned on 4096-byte boundaries.
1561 <para>Disabling the writethrough cache is advisable when files are
1562 mostly written to the file system but are not re-read within a
1563 short time period, or files are only written and re-read by the
1564 same node, regardless of whether the I/O is aligned or not.</para>
1565 <para>To disable writethrough cache on all targets on a server, run:
1568 oss1# lctl set_param osd-*.*.writethrough_cache_enable=0
1570 <para>To re-enable the writethrough cache on one OST, run:</para>
1572 oss1# lctl set_param osd-*.{OST_name}.writethrough_cache_enable=1
1574 <para>To check if the writethrough cache is enabled, run:</para>
1576 oss1# lctl get_param osd-*.*.writethrough_cache_enable
1580 <para><literal>readcache_max_filesize</literal> - Controls the
1581 maximum size of an object that both the read cache and
1582 writethrough cache will try to keep in memory. Objects larger
1583 than <literal>readcache_max_filesize</literal> will not be kept
1584 in cache for either reads or writes regardless of the
1585 <literal>read_cache_enable</literal> or
1586 <literal>writethrough_cache_enable</literal> settings.</para>
1587 <para>Setting this tunable can be useful for workloads where
1588 relatively small objects are repeatedly accessed by many clients,
1589 such as job startup objects, executables, log objects, etc., but
1590 large objects are read or written only once. By not putting the
1591 larger objects into the cache, it is much more likely that more
1592 of the smaller objects will remain in cache for a longer time.
1594 <para>When setting <literal>readcache_max_filesize</literal>,
1595 the input value can be specified in bytes, or can have a suffix
1596 to indicate other binary units such as
1597 <literal>K</literal> (kibibytes),
1598 <literal>M</literal> (mebibytes),
1599 <literal>G</literal> (gibibytes),
1600 <literal>T</literal> (tebibytes), or
1601 <literal>P</literal> (pebibytes).</para>
1603 To limit the maximum cached object size to 64 MiB on all OSTs of
1607 oss1# lctl set_param osd-*.*.readcache_max_filesize=64M
1609 <para>To disable the maximum cached object size on all targets, run:
1612 oss1# lctl set_param osd-*.*.readcache_max_filesize=-1
1615 To check the current maximum cached object size on all targets of
1619 oss1# lctl get_param osd-*.*.readcache_max_filesize
1623 <para><literal>readcache_max_io_mb</literal> - Controls the maximum
1624 size of a single read IO that will be cached in memory. Reads
1625 larger than <literal>readcache_max_io_mb</literal> will be read
1626 directly from storage and bypass the page cache completely.
1627 This avoids significant CPU overhead at high IO rates.
1628 The read cache cannot be disabled for <literal>osd-zfs</literal>,
1629 and as a result this parameter is unavailable for that backend.
1631 <para>When setting <literal>readcache_max_io_mb</literal>, the
1632 input value can be specified in mebibytes, or can have a suffix
1633 to indicate other binary units such as
1634 <literal>K</literal> (kibibytes),
1635 <literal>M</literal> (mebibytes),
1636 <literal>G</literal> (gibibytes),
1637 <literal>T</literal> (tebibytes), or
1638 <literal>P</literal> (pebibytes).</para>
1641 <para><literal>writethrough_max_io_mb</literal> - Controls the
1642 maximum size of a single writes IO that will be cached in memory.
1643 Writes larger than <literal>writethrough_max_io_mb</literal> will
1644 be written directly to storage and bypass the page cache entirely.
1645 This avoids significant CPU overhead at high IO rates.
1646 The write cache cannot be disabled for <literal>osd-zfs</literal>,
1647 and as a result this parameter is unavailable for that backend.
1649 <para>When setting <literal>writethrough_max_io_mb</literal>, the
1650 input value can be specified in mebibytes, or can have a suffix
1651 to indicate other binary units such as
1652 <literal>K</literal> (kibibytes),
1653 <literal>M</literal> (mebibytes),
1654 <literal>G</literal> (gibibytes),
1655 <literal>T</literal> (tebibytes), or
1656 <literal>P</literal> (pebibytes).</para>
1663 <primary>proc</primary>
1664 <secondary>OSS journal</secondary>
1665 </indexterm>Enabling OSS Asynchronous Journal Commit</title>
1666 <para>The OSS asynchronous journal commit feature asynchronously writes data to disk without
1667 forcing a journal flush. This reduces the number of seeks and significantly improves
1668 performance on some hardware.</para>
1670 <para>Asynchronous journal commit cannot work with direct I/O-originated writes
1671 (<literal>O_DIRECT</literal> flag set). In this case, a journal flush is forced. </para>
1673 <para>When the asynchronous journal commit feature is enabled, client nodes keep data in the
1674 page cache (a page reference). Lustre clients monitor the last committed transaction number
1675 (<literal>transno</literal>) in messages sent from the OSS to the clients. When a client
1676 sees that the last committed <literal>transno</literal> reported by the OSS is at least
1677 equal to the bulk write <literal>transno</literal>, it releases the reference on the
1678 corresponding pages. To avoid page references being held for too long on clients after a
1679 bulk write, a 7 second ping request is scheduled (the default OSS file system commit time
1680 interval is 5 seconds) after the bulk write reply is received, so the OSS has an opportunity
1681 to report the last committed <literal>transno</literal>.</para>
1682 <para>If the OSS crashes before the journal commit occurs, then intermediate data is lost.
1683 However, OSS recovery functionality incorporated into the asynchronous journal commit
1684 feature causes clients to replay their write requests and compensate for the missing disk
1685 updates by restoring the state of the file system.</para>
1686 <para>By default, <literal>sync_journal</literal> is enabled
1687 (<literal>sync_journal=1</literal>), so that journal entries are committed synchronously.
1688 To enable asynchronous journal commit, set the <literal>sync_journal</literal> parameter to
1689 <literal>0</literal> by entering: </para>
1690 <screen>$ lctl set_param obdfilter.*.sync_journal=0
1691 obdfilter.lol-OST0001.sync_journal=0</screen>
1692 <para>An associated <literal>sync-on-lock-cancel</literal> feature (enabled by default)
1693 addresses a data consistency issue that can result if an OSS crashes after multiple clients
1694 have written data into intersecting regions of an object, and then one of the clients also
1695 crashes. A condition is created in which the POSIX requirement for continuous writes is
1696 violated along with a potential for corrupted data. With
1697 <literal>sync-on-lock-cancel</literal> enabled, if a cancelled lock has any volatile
1698 writes attached to it, the OSS synchronously writes the journal to disk on lock
1699 cancellation. Disabling the <literal>sync-on-lock-cancel</literal> feature may enhance
1700 performance for concurrent write workloads, but it is recommended that you not disable this
1702 <para> The <literal>sync_on_lock_cancel</literal> parameter can be set to the following
1706 <para><literal>always</literal> - Always force a journal flush on lock cancellation
1707 (default when <literal>async_journal</literal> is enabled).</para>
1710 <para><literal>blocking</literal> - Force a journal flush only when the local cancellation
1711 is due to a blocking callback.</para>
1714 <para><literal>never</literal> - Do not force any journal flush (default when
1715 <literal>async_journal</literal> is disabled).</para>
1718 <para>For example, to set <literal>sync_on_lock_cancel</literal> to not to force a journal
1719 flush, use a command similar to:</para>
1720 <screen>$ lctl get_param obdfilter.*.sync_on_lock_cancel
1721 obdfilter.lol-OST0001.sync_on_lock_cancel=never</screen>
1723 <section xml:id="dbdoclet.TuningModRPCs" condition='l28'>
1726 <primary>proc</primary>
1727 <secondary>client metadata performance</secondary>
1729 Tuning the Client Metadata RPC Stream
1731 <para>The client metadata RPC stream represents the metadata RPCs issued
1732 in parallel by a client to a MDT target. The metadata RPCs can be split
1733 in two categories: the requests that do not modify the file system
1734 (like getattr operation), and the requests that do modify the file system
1735 (like create, unlink, setattr operations). To help optimize the client
1736 metadata RPC stream, several tuning variables are provided to adjust
1737 behavior according to network conditions and cluster size.</para>
1738 <para>Note that increasing the number of metadata RPCs issued in parallel
1739 might improve the performance metadata intensive parallel applications,
1740 but as a consequence it will consume more memory on the client and on
1743 <title>Configuring the Client Metadata RPC Stream</title>
1744 <para>The MDC <literal>max_rpcs_in_flight</literal> parameter defines
1745 the maximum number of metadata RPCs, both modifying and
1746 non-modifying RPCs, that can be sent in parallel by a client to a MDT
1747 target. This includes every file system metadata operations, such as
1748 file or directory stat, creation, unlink. The default setting is 8,
1749 minimum setting is 1 and maximum setting is 256.</para>
1750 <para>To set the <literal>max_rpcs_in_flight</literal> parameter, run
1751 the following command on the Lustre client:</para>
1752 <screen>client$ lctl set_param mdc.*.max_rpcs_in_flight=16</screen>
1753 <para>The MDC <literal>max_mod_rpcs_in_flight</literal> parameter
1754 defines the maximum number of file system modifying RPCs that can be
1755 sent in parallel by a client to a MDT target. For example, the Lustre
1756 client sends modify RPCs when it performs file or directory creation,
1757 unlink, access permission modification or ownership modification. The
1758 default setting is 7, minimum setting is 1 and maximum setting is
1760 <para>To set the <literal>max_mod_rpcs_in_flight</literal> parameter,
1761 run the following command on the Lustre client:</para>
1762 <screen>client$ lctl set_param mdc.*.max_mod_rpcs_in_flight=12</screen>
1763 <para>The <literal>max_mod_rpcs_in_flight</literal> value must be
1764 strictly less than the <literal>max_rpcs_in_flight</literal> value.
1765 It must also be less or equal to the MDT
1766 <literal>max_mod_rpcs_per_client</literal> value. If one of theses
1767 conditions is not enforced, the setting fails and an explicit message
1768 is written in the Lustre log.</para>
1769 <para>The MDT <literal>max_mod_rpcs_per_client</literal> parameter is a
1770 tunable of the kernel module <literal>mdt</literal> that defines the
1771 maximum number of file system modifying RPCs in flight allowed per
1772 client. The parameter can be updated at runtime, but the change is
1773 effective to new client connections only. The default setting is 8.
1775 <para>To set the <literal>max_mod_rpcs_per_client</literal> parameter,
1776 run the following command on the MDS:</para>
1777 <screen>mds$ echo 12 > /sys/module/mdt/parameters/max_mod_rpcs_per_client</screen>
1780 <title>Monitoring the Client Metadata RPC Stream</title>
1781 <para>The <literal>rpc_stats</literal> file contains histogram data
1782 showing information about modify metadata RPCs. It can be helpful to
1783 identify the level of parallelism achieved by an application doing
1784 modify metadata operations.</para>
1785 <para><emphasis role="bold">Example:</emphasis></para>
1786 <screen>client$ lctl get_param mdc.*.rpc_stats
1787 snapshot_time: 1441876896.567070 (secs.usecs)
1788 modify_RPCs_in_flight: 0
1791 rpcs in flight rpcs % cum %
1804 12: 4540 18 100</screen>
1805 <para>The file information includes:</para>
1808 <para><literal>snapshot_time</literal> - UNIX epoch instant the
1809 file was read.</para>
1812 <para><literal>modify_RPCs_in_flight</literal> - Number of modify
1813 RPCs issued by the MDC, but not completed at the time of the
1814 snapshot. This value should always be less than or equal to
1815 <literal>max_mod_rpcs_in_flight</literal>.</para>
1818 <para><literal>rpcs in flight</literal> - Number of modify RPCs
1819 that are pending when a RPC is sent, the relative percentage
1820 (<literal>%</literal>) of total modify RPCs, and the cumulative
1821 percentage (<literal>cum %</literal>) to that point.</para>
1824 <para>If a large proportion of modify metadata RPCs are issued with a
1825 number of pending metadata RPCs close to the
1826 <literal>max_mod_rpcs_in_flight</literal> value, it means the
1827 <literal>max_mod_rpcs_in_flight</literal> value could be increased to
1828 improve the modify metadata performance.</para>
1833 <title>Configuring Timeouts in a Lustre File System</title>
1834 <para>In a Lustre file system, RPC timeouts are set using an adaptive timeouts mechanism, which
1835 is enabled by default. Servers track RPC completion times and then report back to clients
1836 estimates for completion times for future RPCs. Clients use these estimates to set RPC
1837 timeout values. If the processing of server requests slows down for any reason, the server
1838 estimates for RPC completion increase, and clients then revise RPC timeout values to allow
1839 more time for RPC completion.</para>
1840 <para>If the RPCs queued on the server approach the RPC timeout specified by the client, to
1841 avoid RPC timeouts and disconnect/reconnect cycles, the server sends an "early reply" to the
1842 client, telling the client to allow more time. Conversely, as server processing speeds up, RPC
1843 timeout values decrease, resulting in faster detection if the server becomes non-responsive
1844 and quicker connection to the failover partner of the server.</para>
1847 <primary>proc</primary>
1848 <secondary>configuring adaptive timeouts</secondary>
1849 </indexterm><indexterm>
1850 <primary>configuring</primary>
1851 <secondary>adaptive timeouts</secondary>
1852 </indexterm><indexterm>
1853 <primary>proc</primary>
1854 <secondary>adaptive timeouts</secondary>
1855 </indexterm>Configuring Adaptive Timeouts</title>
1856 <para>The adaptive timeout parameters in the table below can be set persistently system-wide
1857 using <literal>lctl conf_param</literal> on the MGS. For example, the following command sets
1858 the <literal>at_max</literal> value for all servers and clients associated with the file
1860 <literal>testfs</literal>:<screen>lctl conf_param testfs.sys.at_max=1500</screen></para>
1862 <para>Clients that access multiple Lustre file systems must use the same parameter values
1863 for all file systems.</para>
1865 <informaltable frame="all">
1867 <colspec colname="c1" colwidth="30*"/>
1868 <colspec colname="c2" colwidth="80*"/>
1872 <para><emphasis role="bold">Parameter</emphasis></para>
1875 <para><emphasis role="bold">Description</emphasis></para>
1883 <literal> at_min </literal></para>
1886 <para>Minimum adaptive timeout (in seconds). The default value is 0. The
1887 <literal>at_min</literal> parameter is the minimum processing time that a server
1888 will report. Ideally, <literal>at_min</literal> should be set to its default
1889 value. Clients base their timeouts on this value, but they do not use this value
1891 <para>If, for unknown reasons (usually due to temporary network outages), the
1892 adaptive timeout value is too short and clients time out their RPCs, you can
1893 increase the <literal>at_min</literal> value to compensate for this.</para>
1899 <literal> at_max </literal></para>
1902 <para>Maximum adaptive timeout (in seconds). The <literal>at_max</literal> parameter
1903 is an upper-limit on the service time estimate. If <literal>at_max</literal> is
1904 reached, an RPC request times out.</para>
1905 <para>Setting <literal>at_max</literal> to 0 causes adaptive timeouts to be disabled
1906 and a fixed timeout method to be used instead (see <xref
1907 xmlns:xlink="http://www.w3.org/1999/xlink" linkend="section_c24_nt5_dl"/></para>
1909 <para>If slow hardware causes the service estimate to increase beyond the default
1910 value of <literal>at_max</literal>, increase <literal>at_max</literal> to the
1911 maximum time you are willing to wait for an RPC completion.</para>
1918 <literal> at_history </literal></para>
1921 <para>Time period (in seconds) within which adaptive timeouts remember the slowest
1922 event that occurred. The default is 600.</para>
1928 <literal> at_early_margin </literal></para>
1931 <para>Amount of time before the Lustre server sends an early reply (in seconds).
1932 Default is 5.</para>
1938 <literal> at_extra </literal></para>
1941 <para>Incremental amount of time that a server requests with each early reply (in
1942 seconds). The server does not know how much time the RPC will take, so it asks for
1943 a fixed value. The default is 30, which provides a balance between sending too
1944 many early replies for the same RPC and overestimating the actual completion
1946 <para>When a server finds a queued request about to time out and needs to send an
1947 early reply out, the server adds the <literal>at_extra</literal> value. If the
1948 time expires, the Lustre server drops the request, and the client enters recovery
1949 status and reconnects to restore the connection to normal status.</para>
1950 <para>If you see multiple early replies for the same RPC asking for 30-second
1951 increases, change the <literal>at_extra</literal> value to a larger number to cut
1952 down on early replies sent and, therefore, network load.</para>
1958 <literal> ldlm_enqueue_min </literal></para>
1961 <para>Minimum lock enqueue time (in seconds). The default is 100. The time it takes
1962 to enqueue a lock, <literal>ldlm_enqueue</literal>, is the maximum of the measured
1963 enqueue estimate (influenced by <literal>at_min</literal> and
1964 <literal>at_max</literal> parameters), multiplied by a weighting factor and the
1965 value of <literal>ldlm_enqueue_min</literal>. </para>
1966 <para>Lustre Distributed Lock Manager (LDLM) lock enqueues have a dedicated minimum
1967 value for <literal>ldlm_enqueue_min</literal>. Lock enqueue timeouts increase as
1968 the measured enqueue times increase (similar to adaptive timeouts).</para>
1975 <title>Interpreting Adaptive Timeout Information</title>
1976 <para>Adaptive timeout information can be obtained via
1977 <literal>lctl get_param {osc,mdc}.*.timeouts</literal> files on each
1978 client and <literal>lctl get_param {ost,mds}.*.*.timeouts</literal>
1979 on each server. To read information from a
1980 <literal>timeouts</literal> file, enter a command similar to:</para>
1981 <screen># lctl get_param -n ost.*.ost_io.timeouts
1982 service : cur 33 worst 34 (at 1193427052, 1600s ago) 1 1 33 2</screen>
1983 <para>In this example, the <literal>ost_io</literal> service on this
1984 node is currently reporting an estimated RPC service time of 33
1985 seconds. The worst RPC service time was 34 seconds, which occurred
1986 26 minutes ago.</para>
1987 <para>The output also provides a history of service times.
1988 Four "bins" of adaptive timeout history are shown, with the
1989 maximum RPC time in each bin reported. In both the 0-150s bin and the
1990 150-300s bin, the maximum RPC time was 1. The 300-450s bin shows the
1991 worst (maximum) RPC time at 33 seconds, and the 450-600s bin shows a
1992 maximum of RPC time of 2 seconds. The estimated service time is the
1993 maximum value in the four bins (33 seconds in this example).</para>
1994 <para>Service times (as reported by the servers) are also tracked in
1995 the client OBDs, as shown in this example:</para>
1996 <screen># lctl get_param osc.*.timeouts
1997 last reply : 1193428639, 0d0h00m00s ago
1998 network : cur 1 worst 2 (at 1193427053, 0d0h26m26s ago) 1 1 1 1
1999 portal 6 : cur 33 worst 34 (at 1193427052, 0d0h26m27s ago) 33 33 33 2
2000 portal 28 : cur 1 worst 1 (at 1193426141, 0d0h41m38s ago) 1 1 1 1
2001 portal 7 : cur 1 worst 1 (at 1193426141, 0d0h41m38s ago) 1 0 1 1
2002 portal 17 : cur 1 worst 1 (at 1193426177, 0d0h41m02s ago) 1 0 0 1
2004 <para>In this example, portal 6, the <literal>ost_io</literal> service
2005 portal, shows the history of service estimates reported by the portal.
2007 <para>Server statistic files also show the range of estimates including
2008 min, max, sum, and sum-squared. For example:</para>
2009 <screen># lctl get_param mdt.*.mdt.stats
2011 req_timeout 6 samples [sec] 1 10 15 105
2016 <section xml:id="section_c24_nt5_dl">
2017 <title>Setting Static Timeouts<indexterm>
2018 <primary>proc</primary>
2019 <secondary>static timeouts</secondary>
2020 </indexterm></title>
2021 <para>The Lustre software provides two sets of static (fixed) timeouts, LND timeouts and
2022 Lustre timeouts, which are used when adaptive timeouts are not enabled.</para>
2026 <para><emphasis role="italic"><emphasis role="bold">LND timeouts</emphasis></emphasis> -
2027 LND timeouts ensure that point-to-point communications across a network complete in a
2028 finite time in the presence of failures, such as packages lost or broken connections.
2029 LND timeout parameters are set for each individual LND.</para>
2030 <para>LND timeouts are logged with the <literal>S_LND</literal> flag set. They are not
2031 printed as console messages, so check the Lustre log for <literal>D_NETERROR</literal>
2032 messages or enable printing of <literal>D_NETERROR</literal> messages to the console
2033 using:<screen>lctl set_param printk=+neterror</screen></para>
2034 <para>Congested routers can be a source of spurious LND timeouts. To avoid this
2035 situation, increase the number of LNet router buffers to reduce back-pressure and/or
2036 increase LND timeouts on all nodes on all connected networks. Also consider increasing
2037 the total number of LNet router nodes in the system so that the aggregate router
2038 bandwidth matches the aggregate server bandwidth.</para>
2041 <para><emphasis role="italic"><emphasis role="bold">Lustre timeouts
2042 </emphasis></emphasis>- Lustre timeouts ensure that Lustre RPCs complete in a finite
2043 time in the presence of failures when adaptive timeouts are not enabled. Adaptive
2044 timeouts are enabled by default. To disable adaptive timeouts at run time, set
2045 <literal>at_max</literal> to 0 by running on the
2046 MGS:<screen># lctl conf_param <replaceable>fsname</replaceable>.sys.at_max=0</screen></para>
2048 <para>Changing the status of adaptive timeouts at runtime may cause a transient client
2049 timeout, recovery, and reconnection.</para>
2051 <para>Lustre timeouts are always printed as console messages. </para>
2052 <para>If Lustre timeouts are not accompanied by LND timeouts, increase the Lustre
2053 timeout on both servers and clients. Lustre timeouts are set using a command such as
2054 the following:<screen># lctl set_param timeout=30</screen></para>
2055 <para>Lustre timeout parameters are described in the table below.</para>
2058 <informaltable frame="all">
2060 <colspec colname="c1" colnum="1" colwidth="30*"/>
2061 <colspec colname="c2" colnum="2" colwidth="70*"/>
2064 <entry>Parameter</entry>
2065 <entry>Description</entry>
2070 <entry><literal>timeout</literal></entry>
2072 <para>The time that a client waits for a server to complete an RPC (default 100s).
2073 Servers wait half this time for a normal client RPC to complete and a quarter of
2074 this time for a single bulk request (read or write of up to 4 MB) to complete.
2075 The client pings recoverable targets (MDS and OSTs) at one quarter of the
2076 timeout, and the server waits one and a half times the timeout before evicting a
2077 client for being "stale."</para>
2078 <para>Lustre client sends periodic 'ping' messages to servers with which
2079 it has had no communication for the specified period of time. Any network
2080 activity between a client and a server in the file system also serves as a
2085 <entry><literal>ldlm_timeout</literal></entry>
2087 <para>The time that a server waits for a client to reply to an initial AST (lock
2088 cancellation request). The default is 20s for an OST and 6s for an MDS. If the
2089 client replies to the AST, the server will give it a normal timeout (half the
2090 client timeout) to flush any dirty data and release the lock.</para>
2094 <entry><literal>fail_loc</literal></entry>
2096 <para>An internal debugging failure hook. The default value of
2097 <literal>0</literal> means that no failure will be triggered or
2102 <entry><literal>dump_on_timeout</literal></entry>
2104 <para>Triggers a dump of the Lustre debug log when a timeout occurs. The default
2105 value of <literal>0</literal> (zero) means a dump of the Lustre debug log will
2106 not be triggered.</para>
2110 <entry><literal>dump_on_eviction</literal></entry>
2112 <para>Triggers a dump of the Lustre debug log when an eviction occurs. The default
2113 value of <literal>0</literal> (zero) means a dump of the Lustre debug log will
2114 not be triggered. </para>
2123 <section remap="h3">
2125 <primary>proc</primary>
2126 <secondary>LNet</secondary>
2127 </indexterm><indexterm>
2128 <primary>LNet</primary>
2129 <secondary>proc</secondary>
2130 </indexterm>Monitoring LNet</title>
2131 <para>LNet information is located via <literal>lctl get_param</literal>
2132 in these parameters:
2135 <para><literal>peers</literal> - Shows all NIDs known to this node
2136 and provides information on the queue state.</para>
2137 <para>Example:</para>
2138 <screen># lctl get_param peers
2139 nid refs state max rtr min tx min queue
2140 0@lo 1 ~rtr 0 0 0 0 0 0
2141 192.168.10.35@tcp 1 ~rtr 8 8 8 8 6 0
2142 192.168.10.36@tcp 1 ~rtr 8 8 8 8 6 0
2143 192.168.10.37@tcp 1 ~rtr 8 8 8 8 6 0</screen>
2144 <para>The fields are explained in the table below:</para>
2145 <informaltable frame="all">
2147 <colspec colname="c1" colwidth="30*"/>
2148 <colspec colname="c2" colwidth="80*"/>
2152 <para><emphasis role="bold">Field</emphasis></para>
2155 <para><emphasis role="bold">Description</emphasis></para>
2163 <literal>refs</literal>
2167 <para>A reference count. </para>
2173 <literal>state</literal>
2177 <para>If the node is a router, indicates the state of the router. Possible
2181 <para><literal>NA</literal> - Indicates the node is not a router.</para>
2184 <para><literal>up/down</literal>- Indicates if the node (router) is up or
2193 <literal>max </literal></para>
2196 <para>Maximum number of concurrent sends from this peer.</para>
2202 <literal>rtr </literal></para>
2205 <para>Number of available routing buffer credits.</para>
2211 <literal>min </literal></para>
2214 <para>Minimum number of routing buffer credits seen.</para>
2220 <literal>tx </literal></para>
2223 <para>Number of available send credits.</para>
2229 <literal>min </literal></para>
2232 <para>Minimum number of send credits seen.</para>
2238 <literal>queue </literal></para>
2241 <para>Total bytes in active/queued sends.</para>
2247 <para>Credits are initialized to allow a certain number of operations
2248 (in the example above the table, eight as shown in the
2249 <literal>max</literal> column. LNet keeps track of the minimum
2250 number of credits ever seen over time showing the peak congestion
2251 that has occurred during the time monitored. Fewer available credits
2252 indicates a more congested resource. </para>
2253 <para>The number of credits currently available is shown in the
2254 <literal>tx</literal> column. The maximum number of send credits is
2255 shown in the <literal>max</literal> column and never changes. The
2256 number of currently active transmits can be derived by
2257 <literal>(max - tx)</literal>, as long as
2258 <literal>tx</literal> is greater than or equal to 0. Once
2259 <literal>tx</literal> is less than 0, it indicates the number of
2260 transmits on that peer which have been queued for lack of credits.
2262 <para>The number of router buffer credits available for consumption
2263 by a peer is shown in <literal>rtr</literal> column. The number of
2264 routing credits can be configured separately at the LND level or at
2265 the LNet level by using the <literal>peer_buffer_credits</literal>
2266 module parameter for the appropriate module. If the routing credits
2267 is not set explicitly, it'll default to the maximum transmit credits
2268 defined by <literal>peer_credits</literal> module parameter.
2269 Whenever a gateway routes a message from a peer, it decrements the
2270 number of available routing credits for that peer. If that value
2271 goes to zero, then messages will be queued. Negative values show the
2272 number of queued message waiting to be routed. The number of
2273 messages which are currently being routed from a peer can be derived
2274 by <literal>(max_rtr_credits - rtr)</literal>.</para>
2275 <para>LNet also limits concurrent sends and number of router buffers
2276 allocated to a single peer so that no peer can occupy all resources.
2280 <para><literal>nis</literal> - Shows current queue health on the node.
2282 <para>Example:</para>
2283 <screen># lctl get_param nis
2284 nid refs peer max tx min
2286 192.168.10.34@tcp 4 8 256 256 252
2288 <para> The fields are explained in the table below.</para>
2289 <informaltable frame="all">
2291 <colspec colname="c1" colwidth="30*"/>
2292 <colspec colname="c2" colwidth="80*"/>
2296 <para><emphasis role="bold">Field</emphasis></para>
2299 <para><emphasis role="bold">Description</emphasis></para>
2307 <literal> nid </literal></para>
2310 <para>Network interface.</para>
2316 <literal> refs </literal></para>
2319 <para>Internal reference counter.</para>
2325 <literal> peer </literal></para>
2328 <para>Number of peer-to-peer send credits on this NID. Credits are used to size
2329 buffer pools.</para>
2335 <literal> max </literal></para>
2338 <para>Total number of send credits on this NID.</para>
2344 <literal> tx </literal></para>
2347 <para>Current number of send credits available on this NID.</para>
2353 <literal> min </literal></para>
2356 <para>Lowest number of send credits available on this NID.</para>
2362 <literal> queue </literal></para>
2365 <para>Total bytes in active/queued sends.</para>
2371 <para><emphasis role="bold"><emphasis role="italic">Analysis:</emphasis></emphasis></para>
2372 <para>Subtracting <literal>max</literal> from <literal>tx</literal>
2373 (<literal>max</literal> - <literal>tx</literal>) yields the number of sends currently
2374 active. A large or increasing number of active sends may indicate a problem.</para>
2376 </itemizedlist></para>
2378 <section remap="h3" xml:id="dbdoclet.balancing_free_space">
2380 <primary>proc</primary>
2381 <secondary>free space</secondary>
2382 </indexterm>Allocating Free Space on OSTs</title>
2383 <para>Free space is allocated using either a round-robin or a weighted
2384 algorithm. The allocation method is determined by the maximum amount of
2385 free-space imbalance between the OSTs. When free space is relatively
2386 balanced across OSTs, the faster round-robin allocator is used, which
2387 maximizes network balancing. The weighted allocator is used when any two
2388 OSTs are out of balance by more than a specified threshold.</para>
2389 <para>Free space distribution can be tuned using these two
2390 tunable parameters:</para>
2393 <para><literal>lod.*.qos_threshold_rr</literal> - The threshold at which
2394 the allocation method switches from round-robin to weighted is set
2395 in this file. The default is to switch to the weighted algorithm when
2396 any two OSTs are out of balance by more than 17 percent.</para>
2399 <para><literal>lod.*.qos_prio_free</literal> - The weighting priority
2400 used by the weighted allocator can be adjusted in this file. Increasing
2401 the value of <literal>qos_prio_free</literal> puts more weighting on the
2402 amount of free space available on each OST and less on how stripes are
2403 distributed across OSTs. The default value is 91 percent weighting for
2404 free space rebalancing and 9 percent for OST balancing. When the
2405 free space priority is set to 100, weighting is based entirely on free
2406 space and location is no longer used by the striping algorithm.</para>
2409 <para condition="l29"><literal>osp.*.reserved_mb_low</literal>
2410 - The low watermark used to stop object allocation if available space
2411 is less than this. The default is 0.1% of total OST size.</para>
2414 <para condition="l29"><literal>osp.*.reserved_mb_high</literal>
2415 - The high watermark used to start object allocation if available
2416 space is more than this. The default is 0.2% of total OST size.</para>
2419 <para>For more information about monitoring and managing free space, see
2420 <xref xmlns:xlink="http://www.w3.org/1999/xlink"
2421 linkend="file_striping.managing_free_space"/>.</para>
2423 <section remap="h3">
2425 <primary>proc</primary>
2426 <secondary>locking</secondary>
2427 </indexterm>Configuring Locking</title>
2428 <para>The <literal>lru_size</literal> parameter is used to control the
2429 number of client-side locks in the LRU cached locks queue. LRU size is
2430 normally dynamic, based on load to optimize the number of locks cached
2431 on nodes that have different workloads (e.g., login/build nodes vs.
2432 compute nodes vs. backup nodes).</para>
2433 <para>The total number of locks available is a function of the server RAM.
2434 The default limit is 50 locks/1 MB of RAM. If memory pressure is too high,
2435 the LRU size is shrunk. The number of locks on the server is limited to
2436 <replaceable>num_osts_per_oss * num_clients * lru_size</replaceable>
2440 <para>To enable automatic LRU sizing, set the
2441 <literal>lru_size</literal> parameter to 0. In this case, the
2442 <literal>lru_size</literal> parameter shows the current number of locks
2443 being used on the client. Dynamic LRU resizing is enabled by default.
2447 <para>To specify a maximum number of locks, set the
2448 <literal>lru_size</literal> parameter to a value other than zero.
2449 A good default value for compute nodes is around
2450 <literal>100 * <replaceable>num_cpus</replaceable></literal>.
2451 It is recommended that you only set <literal>lru_size</literal>
2452 to be signifivantly larger on a few login nodes where multiple
2453 users access the file system interactively.</para>
2456 <para>To clear the LRU on a single client, and, as a result, flush client
2457 cache without changing the <literal>lru_size</literal> value, run:</para>
2458 <screen># lctl set_param ldlm.namespaces.<replaceable>osc_name|mdc_name</replaceable>.lru_size=clear</screen>
2459 <para>If the LRU size is set lower than the number of existing locks,
2460 <emphasis>unused</emphasis> locks are canceled immediately. Use
2461 <literal>clear</literal> to cancel all locks without changing the value.
2464 <para>The <literal>lru_size</literal> parameter can only be set
2465 temporarily using <literal>lctl set_param</literal>, it cannot be set
2468 <para>To disable dynamic LRU resizing on the clients, run for example:
2470 <screen># lctl set_param ldlm.namespaces.*osc*.lru_size=5000</screen>
2471 <para>To determine the number of locks being granted with dynamic LRU
2472 resizing, run:</para>
2473 <screen>$ lctl get_param ldlm.namespaces.*.pool.limit</screen>
2474 <para>The <literal>lru_max_age</literal> parameter is used to control the
2475 age of client-side locks in the LRU cached locks queue. This limits how
2476 long unused locks are cached on the client, and avoids idle clients from
2477 holding locks for an excessive time, which reduces memory usage on both
2478 the client and server, as well as reducing work during server recovery.
2480 <para>The <literal>lru_max_age</literal> is set and printed in milliseconds,
2481 and by default is 3900000 ms (65 minutes).</para>
2482 <para condition='l2B'>Since Lustre 2.11, in addition to setting the
2483 maximum lock age in milliseconds, it can also be set using a suffix of
2484 <literal>s</literal> or <literal>ms</literal> to indicate seconds or
2485 milliseconds, respectively. For example to set the client's maximum
2486 lock age to 15 minutes (900s) run:
2489 # lctl set_param ldlm.namespaces.*MDT*.lru_max_age=900s
2490 # lctl get_param ldlm.namespaces.*MDT*.lru_max_age
2491 ldlm.namespaces.myth-MDT0000-mdc-ffff8804296c2800.lru_max_age=900000
2494 <section xml:id="dbdoclet.tuning_setting_thread_count">
2496 <primary>proc</primary>
2497 <secondary>thread counts</secondary>
2498 </indexterm>Setting MDS and OSS Thread Counts</title>
2499 <para>MDS and OSS thread counts tunable can be used to set the minimum and maximum thread counts
2500 or get the current number of running threads for the services listed in the table
2502 <informaltable frame="all">
2504 <colspec colname="c1" colwidth="50*"/>
2505 <colspec colname="c2" colwidth="50*"/>
2510 <emphasis role="bold">Service</emphasis></para>
2514 <emphasis role="bold">Description</emphasis></para>
2519 <literal> mds.MDS.mdt </literal>
2522 <para>Main metadata operations service</para>
2527 <literal> mds.MDS.mdt_readpage </literal>
2530 <para>Metadata <literal>readdir</literal> service</para>
2535 <literal> mds.MDS.mdt_setattr </literal>
2538 <para>Metadata <literal>setattr/close</literal> operations service </para>
2543 <literal> ost.OSS.ost </literal>
2546 <para>Main data operations service</para>
2551 <literal> ost.OSS.ost_io </literal>
2554 <para>Bulk data I/O services</para>
2559 <literal> ost.OSS.ost_create </literal>
2562 <para>OST object pre-creation service</para>
2567 <literal> ldlm.services.ldlm_canceld </literal>
2570 <para>DLM lock cancel service</para>
2575 <literal> ldlm.services.ldlm_cbd </literal>
2578 <para>DLM lock grant service</para>
2584 <para>For each service, tunable parameters as shown below are available.
2588 <para>To temporarily set these tunables, run:</para>
2589 <screen># lctl set_param <replaceable>service</replaceable>.threads_<replaceable>min|max|started=num</replaceable> </screen>
2592 <para>To permanently set this tunable, run the following command on
2594 <screen>mgs# lctl set_param -P <replaceable>service</replaceable>.threads_<replaceable>min|max|started</replaceable></screen></para>
2595 <para condition='l25'>For Lustre 2.5 or earlier, run:
2596 <screen>mgs# lctl conf_param <replaceable>obdname|fsname.obdtype</replaceable>.threads_<replaceable>min|max|started</replaceable></screen>
2600 <para>The following examples show how to set thread counts and get the
2601 number of running threads for the service <literal>ost_io</literal>
2603 <literal><replaceable>service</replaceable>.threads_<replaceable>min|max|started</replaceable></literal>.</para>
2606 <para>To get the number of running threads, run:</para>
2607 <screen># lctl get_param ost.OSS.ost_io.threads_started
2608 ost.OSS.ost_io.threads_started=128</screen>
2611 <para>To set the number of threads to the maximum value (512), run:</para>
2612 <screen># lctl get_param ost.OSS.ost_io.threads_max
2613 ost.OSS.ost_io.threads_max=512</screen>
2616 <para>To set the maximum thread count to 256 instead of 512 (to avoid overloading the
2617 storage or for an array with requests), run:</para>
2618 <screen># lctl set_param ost.OSS.ost_io.threads_max=256
2619 ost.OSS.ost_io.threads_max=256</screen>
2622 <para>To set the maximum thread count to 256 instead of 512 permanently, run:</para>
2623 <screen># lctl conf_param testfs.ost.ost_io.threads_max=256</screen>
2624 <para condition='l25'>For version 2.5 or later, run:
2625 <screen># lctl set_param -P ost.OSS.ost_io.threads_max=256
2626 ost.OSS.ost_io.threads_max=256 </screen> </para>
2629 <para> To check if the <literal>threads_max</literal> setting is active, run:</para>
2630 <screen># lctl get_param ost.OSS.ost_io.threads_max
2631 ost.OSS.ost_io.threads_max=256</screen>
2635 <para>If the number of service threads is changed while the file system is running, the change
2636 may not take effect until the file system is stopped and rest. If the number of service
2637 threads in use exceeds the new <literal>threads_max</literal> value setting, service threads
2638 that are already running will not be stopped.</para>
2640 <para>See also <xref xmlns:xlink="http://www.w3.org/1999/xlink" linkend="lustretuning"/></para>
2642 <section xml:id="enabling_interpreting_debugging_logs">
2644 <primary>proc</primary>
2645 <secondary>debug</secondary>
2646 </indexterm>Enabling and Interpreting Debugging Logs</title>
2647 <para>By default, a detailed log of all operations is generated to aid in
2648 debugging. Flags that control debugging are found via
2649 <literal>lctl get_param debug</literal>.</para>
2650 <para>The overhead of debugging can affect the performance of Lustre file
2651 system. Therefore, to minimize the impact on performance, the debug level
2652 can be lowered, which affects the amount of debugging information kept in
2653 the internal log buffer but does not alter the amount of information to
2654 goes into syslog. You can raise the debug level when you need to collect
2655 logs to debug problems. </para>
2656 <para>The debugging mask can be set using "symbolic names". The
2657 symbolic format is shown in the examples below.
2660 <para>To verify the debug level used, examine the parameter that
2661 controls debugging by running:</para>
2662 <screen># lctl get_param debug
2664 ioctl neterror warning error emerg ha config console</screen>
2667 <para>To turn off debugging except for network error debugging, run
2668 the following command on all nodes concerned:</para>
2669 <screen># sysctl -w lnet.debug="neterror"
2670 debug=neterror</screen>
2675 <para>To turn off debugging completely (except for the minimum error
2676 reporting to the console), run the following command on all nodes
2678 <screen># lctl set_param debug=0
2682 <para>To set an appropriate debug level for a production environment,
2684 <screen># lctl set_param debug="warning dlmtrace error emerg ha rpctrace vfstrace"
2685 debug=warning dlmtrace error emerg ha rpctrace vfstrace</screen>
2686 <para>The flags shown in this example collect enough high-level
2687 information to aid debugging, but they do not cause any serious
2688 performance impact.</para>
2693 <para>To add new flags to flags that have already been set,
2694 precede each one with a "<literal>+</literal>":</para>
2695 <screen># lctl set_param debug="+neterror +ha"
2697 # lctl get_param debug
2698 debug=neterror warning error emerg ha console</screen>
2701 <para>To remove individual flags, precede them with a
2702 "<literal>-</literal>":</para>
2703 <screen># lctl set_param debug="-ha"
2705 # lctl get_param debug
2706 debug=neterror warning error emerg console</screen>
2710 <para>Debugging parameters include:</para>
2713 <para><literal>subsystem_debug</literal> - Controls the debug logs for subsystems.</para>
2716 <para><literal>debug_path</literal> - Indicates the location where the debug log is dumped
2717 when triggered automatically or manually. The default path is
2718 <literal>/tmp/lustre-log</literal>.</para>
2721 <para>These parameters can also be set using:<screen>sysctl -w lnet.debug={value}</screen></para>
2722 <para>Additional useful parameters: <itemizedlist>
2724 <para><literal>panic_on_lbug</literal> - Causes ''panic'' to be called
2725 when the Lustre software detects an internal problem (an <literal>LBUG</literal> log
2726 entry); panic crashes the node. This is particularly useful when a kernel crash dump
2727 utility is configured. The crash dump is triggered when the internal inconsistency is
2728 detected by the Lustre software. </para>
2731 <para><literal>upcall</literal> - Allows you to specify the path to the binary which will
2732 be invoked when an <literal>LBUG</literal> log entry is encountered. This binary is
2733 called with four parameters:</para>
2734 <para> - The string ''<literal>LBUG</literal>''.</para>
2735 <para> - The file where the <literal>LBUG</literal> occurred.</para>
2736 <para> - The function name.</para>
2737 <para> - The line number in the file</para>
2739 </itemizedlist></para>
2741 <title>Interpreting OST Statistics</title>
2744 <xref linkend="dbdoclet.50438273_80593"/> (<literal>collectl</literal>).</para>
2746 <para>OST <literal>stats</literal> files can be used to provide statistics showing activity
2747 for each OST. For example:</para>
2748 <screen># lctl get_param osc.testfs-OST0000-osc.stats
2749 snapshot_time 1189732762.835363
2754 obd_ping 212</screen>
2755 <para>Use the <literal>llstat</literal> utility to monitor statistics over time.</para>
2756 <para>To clear the statistics, use the <literal>-c</literal> option to
2757 <literal>llstat</literal>. To specify how frequently the statistics
2758 should be reported (in seconds), use the <literal>-i</literal> option.
2759 In the example below, the <literal>-c</literal> option clears the
2760 statistics and <literal>-i10</literal> option reports statistics every
2762 <screen role="smaller">$ llstat -c -i10 ost_io
2764 /usr/bin/llstat: STATS on 06/06/07
2765 /proc/fs/lustre/ost/OSS/ost_io/ stats on 192.168.16.35@tcp
2766 snapshot_time 1181074093.276072
2768 /proc/fs/lustre/ost/OSS/ost_io/stats @ 1181074103.284895
2770 Count Rate Events Unit last min avg max stddev
2771 req_waittime 8 0 8 [usec] 2078 34 259.75 868 317.49
2772 req_qdepth 8 0 8 [reqs] 1 0 0.12 1 0.35
2773 req_active 8 0 8 [reqs] 11 1 1.38 2 0.52
2774 reqbuf_avail 8 0 8 [bufs] 511 63 63.88 64 0.35
2775 ost_write 8 0 8 [bytes] 169767 72914 212209.62 387579 91874.29
2777 /proc/fs/lustre/ost/OSS/ost_io/stats @ 1181074113.290180
2779 Count Rate Events Unit last min avg max stddev
2780 req_waittime 31 3 39 [usec] 30011 34 822.79 12245 2047.71
2781 req_qdepth 31 3 39 [reqs] 0 0 0.03 1 0.16
2782 req_active 31 3 39 [reqs] 58 1 1.77 3 0.74
2783 reqbuf_avail 31 3 39 [bufs] 1977 63 63.79 64 0.41
2784 ost_write 30 3 38 [bytes] 1028467 15019 315325.16 910694 197776.51
2786 /proc/fs/lustre/ost/OSS/ost_io/stats @ 1181074123.325560
2788 Count Rate Events Unit last min avg max stddev
2789 req_waittime 21 2 60 [usec] 14970 34 784.32 12245 1878.66
2790 req_qdepth 21 2 60 [reqs] 0 0 0.02 1 0.13
2791 req_active 21 2 60 [reqs] 33 1 1.70 3 0.70
2792 reqbuf_avail 21 2 60 [bufs] 1341 63 63.82 64 0.39
2793 ost_write 21 2 59 [bytes] 7648424 15019 332725.08 910694 180397.87
2795 <para>The columns in this example are described in the table below.</para>
2796 <informaltable frame="all">
2798 <colspec colname="c1" colwidth="50*"/>
2799 <colspec colname="c2" colwidth="50*"/>
2803 <para><emphasis role="bold">Parameter</emphasis></para>
2806 <para><emphasis role="bold">Description</emphasis></para>
2812 <entry><literal>Name</literal></entry>
2813 <entry>Name of the service event. See the tables below for descriptions of service
2814 events that are tracked.</entry>
2819 <literal>Cur. Count </literal></para>
2822 <para>Number of events of each type sent in the last interval.</para>
2828 <literal>Cur. Rate </literal></para>
2831 <para>Number of events per second in the last interval.</para>
2837 <literal> # Events </literal></para>
2840 <para>Total number of such events since the events have been cleared.</para>
2846 <literal> Unit </literal></para>
2849 <para>Unit of measurement for that statistic (microseconds, requests,
2856 <literal> last </literal></para>
2859 <para>Average rate of these events (in units/event) for the last interval during
2860 which they arrived. For instance, in the above mentioned case of
2861 <literal>ost_destroy</literal> it took an average of 736 microseconds per
2862 destroy for the 400 object destroys in the previous 10 seconds.</para>
2868 <literal> min </literal></para>
2871 <para>Minimum rate (in units/events) since the service started.</para>
2877 <literal> avg </literal></para>
2880 <para>Average rate.</para>
2886 <literal> max </literal></para>
2889 <para>Maximum rate.</para>
2895 <literal> stddev </literal></para>
2898 <para>Standard deviation (not measured in some cases)</para>
2904 <para>Events common to all services are shown in the table below.</para>
2905 <informaltable frame="all">
2907 <colspec colname="c1" colwidth="50*"/>
2908 <colspec colname="c2" colwidth="50*"/>
2912 <para><emphasis role="bold">Parameter</emphasis></para>
2915 <para><emphasis role="bold">Description</emphasis></para>
2923 <literal> req_waittime </literal></para>
2926 <para>Amount of time a request waited in the queue before being handled by an
2927 available server thread.</para>
2933 <literal> req_qdepth </literal></para>
2936 <para>Number of requests waiting to be handled in the queue for this service.</para>
2942 <literal> req_active </literal></para>
2945 <para>Number of requests currently being handled.</para>
2951 <literal> reqbuf_avail </literal></para>
2954 <para>Number of unsolicited lnet request buffers for this service.</para>
2960 <para>Some service-specific events of interest are described in the table below.</para>
2961 <informaltable frame="all">
2963 <colspec colname="c1" colwidth="50*"/>
2964 <colspec colname="c2" colwidth="50*"/>
2968 <para><emphasis role="bold">Parameter</emphasis></para>
2971 <para><emphasis role="bold">Description</emphasis></para>
2979 <literal> ldlm_enqueue </literal></para>
2982 <para>Time it takes to enqueue a lock (this includes file open on the MDS)</para>
2988 <literal> mds_reint </literal></para>
2991 <para>Time it takes to process an MDS modification record (includes
2992 <literal>create</literal>, <literal>mkdir</literal>, <literal>unlink</literal>,
2993 <literal>rename</literal> and <literal>setattr</literal>)</para>
3001 <title>Interpreting MDT Statistics</title>
3004 <xref linkend="dbdoclet.50438273_80593"/> (<literal>collectl</literal>).</para>
3006 <para>MDT <literal>stats</literal> files can be used to track MDT
3007 statistics for the MDS. The example below shows sample output from an
3008 MDT <literal>stats</literal> file.</para>
3009 <screen># lctl get_param mds.*-MDT0000.stats
3010 snapshot_time 1244832003.676892 secs.usecs
3011 open 2 samples [reqs]
3012 close 1 samples [reqs]
3013 getxattr 3 samples [reqs]
3014 process_config 1 samples [reqs]
3015 connect 2 samples [reqs]
3016 disconnect 2 samples [reqs]
3017 statfs 3 samples [reqs]
3018 setattr 1 samples [reqs]
3019 getattr 3 samples [reqs]
3020 llog_init 6 samples [reqs]
3021 notify 16 samples [reqs]</screen>
3026 vim:expandtab:shiftwidth=2:tabstop=8:
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