<para condition='l24'>If multiple MDTs are going to be present in the
system, each MDT should be specified for the anticipated usage and load.
For details on how to add additional MDTs to the filesystem, see
- <xref linkend="dbdoclet.adding_new_mdt"/>.</para>
+ <xref linkend="lustremaint.adding_new_mdt"/>.</para>
<warning condition='l24'><para>MDT0 contains the root of the Lustre file
system. If MDT0 is unavailable for any reason, the file system cannot be
used.</para></warning>
The size is determined by the total number of servers in the Lustre
file system cluster(s) that are managed by the MGS.</para>
</section>
- <section xml:id="dbdoclet.50438256_87676">
+ <section xml:id="dbdoclet.mdt_space_requirements">
<title><indexterm>
<primary>setup</primary>
<secondary>MDT</secondary>
</indexterm> Determining MDT Space Requirements</title>
<para>When calculating the MDT size, the important factor to consider
is the number of files to be stored in the file system, which depends on
- at least 4 KiB per inode of usable space on the MDT. Since MDTs typically
+ at least 2 KiB per inode of usable space on the MDT. Since MDTs typically
use RAID-1+0 mirroring, the total storage needed will be double this.
</para>
<para>Please note that the actual used space per MDT depends on the number
have ACLs or user xattrs, and the number of hard links per file. The
storage required for Lustre file system metadata is typically 1-2
percent of the total file system capacity depending upon file size.
- If the <xref linkend="dataonmdt.title"/> feature is in use for Lustre
- 2.11 or later, MDT space should typically be 5 percent of the total space,
- depending on the distribution of small files within the filesystem.</para>
+ If the <xref linkend="dataonmdt"/> feature is in use for Lustre
+ 2.11 or later, MDT space should typically be 5 percent or more of the
+ total space, depending on the distribution of small files within the
+ filesystem and the <literal>lod.*.dom_stripesize</literal> limit on
+ the MDT and file layout used.</para>
<para>For ZFS-based MDT filesystems, the number of inodes created on
the MDT and OST is dynamic, so there is less need to determine the
number of inodes in advance, though there still needs to be some thought
given to the total MDT space compared to the total filesystem size.</para>
<para>For example, if the average file size is 5 MiB and you have
- 100 TiB of usable OST space, then you can calculate the minimum total
- number of inodes each for MDTs and OSTs as follows:</para>
+ 100 TiB of usable OST space, then you can calculate the
+ <emphasis>minimum</emphasis> total number of inodes for MDTs and OSTs
+ as follows:</para>
<informalexample>
<para>(500 TB * 1000000 MB/TB) / 5 MB/inode = 100M inodes</para>
</informalexample>
- <para>For details about formatting options for ldiskfs MDT and OST file
- systems, see <xref linkend="dbdoclet.ldiskfs_mdt_mkfs"/>.</para>
- <para>It is recommended that the MDT have at least twice the minimum
+ <para>It is recommended that the MDT(s) have at least twice the minimum
number of inodes to allow for future expansion and allow for an average
- file size smaller than expected. Thus, the minimum space for an ldiskfs
- MDT should be approximately:
+ file size smaller than expected. Thus, the minimum space for ldiskfs
+ MDT(s) should be approximately:
</para>
<informalexample>
<para>2 KiB/inode x 100 million inodes x 2 = 400 GiB ldiskfs MDT</para>
</informalexample>
+ <para>For details about formatting options for ldiskfs MDT and OST file
+ systems, see <xref linkend="dbdoclet.ldiskfs_mdt_mkfs"/>.</para>
<note>
- <para>If the average file size is very small, 4 KB for example, the
- MDT will use as much space for each file as the space used on the OST,
- so the use of Data-on-MDT is strongly recommended.</para>
+ <para>If the median file size is very small, 4 KB for example, the
+ MDT would use as much space for each file as the space used on the OST,
+ so the use of Data-on-MDT is strongly recommended in that case.
+ The MDT space per inode should be increased correspondingly to
+ account for the extra data space usage for each inode:
+ <informalexample>
+ <para>6 KiB/inode x 100 million inodes x 2 = 1200 GiB ldiskfs MDT</para>
+ </informalexample>
+ </para>
</note>
<note>
<para>If the MDT has too few inodes, this can cause the space on the
OSTs to be inaccessible since no new files can be created. In this
- case, the <literal>lfs df -i</literal> and <literal>df -i</literal>
- commands will limit the number of available inodes reported for the
- filesystem to match the total number of available objects on the OSTs.
- Be sure to determine the appropriate MDT size needed to support the
- filesystem before formatting. It is possible to increase the
+ case, the <literal>lfs df -i</literal> and <literal>df -i</literal>
+ commands will limit the number of available inodes reported for the
+ filesystem to match the total number of available objects on the OSTs.
+ Be sure to determine the appropriate MDT size needed to support the
+ filesystem before formatting. It is possible to increase the
number of inodes after the file system is formatted, depending on the
storage. For ldiskfs MDT filesystems the <literal>resize2fs</literal>
tool can be used if the underlying block device is on a LVM logical
</note>
<note condition='l24'>
<para>Starting in release 2.4, using the DNE remote directory feature
- it is possible to increase the total number of inodes of a Lustre
- filesystem, as well as increasing the aggregate metadata performance,
- by configuring additional MDTs into the filesystem, see
- <xref linkend="dbdoclet.adding_new_mdt"/> for details.
+ it is possible to increase the total number of inodes of a Lustre
+ filesystem, as well as increasing the aggregate metadata performance,
+ by configuring additional MDTs into the filesystem, see
+ <xref linkend="lustremaint.adding_new_mdt"/> for details.
</para>
</note>
</section>
such as file layout for files with a large number of stripes, Access
Control Lists (ACLs), and user extended attributes.</para>
<para condition="l2B"> Starting in Lustre 2.11, the <xref linkend=
- "dataonmdt.title"/> feature allows storing small files on the MDT
+ "dataonmdt.title"/> (DoM) feature allows storing small files on the MDT
to take advantage of high-performance flash storage, as well as reduce
space and network overhead. If you are planning to use the DoM feature
with an ldiskfs MDT, it is recommended to <emphasis>increase</emphasis>
- the inode ratio to have enough space on the MDT for small files.</para>
+ the bytes-per-inode ratio to have enough space on the MDT for small files,
+ as described below.
+ </para>
<para>It is possible to change the recommended 2048 bytes
per inode for an ldiskfs MDT when it is first formatted by adding the
<literal>--mkfsoptions="-i bytes-per-inode"</literal> option to
the MDT inode size, which is 1024 bytes by default. It is recommended
to use an inode ratio at least 1024 bytes larger than the inode size to
ensure the MDT does not run out of space. Increasing the inode ratio
- to at least hold the most common file size (e.g. 5120 or 66560 bytes if
- 4KB or 64KB files are widely used) is recommended for DoM.</para>
- <para>The size of the inode may be changed by adding the
+ to include enough space for the most common file data (e.g. 5120 or 65560
+ bytes if 4KB or 64KB files are widely used) is recommended for DoM.</para>
+ <para>The size of the inode may be changed at format time by adding the
<literal>--stripe-count-hint=N</literal> to have
<literal>mkfs.lustre</literal> automatically calculate a reasonable
inode size based on the default stripe count that will be used by the
<literal>--mkfsoptions="-I inode-size"</literal> option. Increasing
the inode size will provide more space in the inode for a larger Lustre
file layout, ACLs, user and system extended attributes, SELinux and
- other security labels, and other internal metadata. However, if these
- features or other in-inode xattrs are not needed, the larger inode size
- will hurt metadata performance as 2x, 4x, or 8x as much data would be
+ other security labels, and other internal metadata and DoM data. However,
+ if these features or other in-inode xattrs are not needed, a larger inode
+ size may hurt metadata performance as 2x, 4x, or 8x as much data would be
read or written for each MDT inode access.
</para>
</section>
<secondary>OST</secondary>
</indexterm>Setting Formatting Options for an ldiskfs OST</title>
<para>When formatting an OST file system, it can be beneficial
- to take local file system usage into account. When doing so, try to
- reduce the number of inodes on each OST, while keeping enough margin
- for potential variations in future usage. This helps reduce the format
- and file system check time and makes more space available for data.</para>
+ to take local file system usage into account, for example by running
+ <literal>df</literal> and <literal>df -i</literal> on a current filesystem
+ to get the used bytes and used inodes respectively, then computing the
+ average bytes-per-inode value. When deciding on the ratio for a new
+ filesystem, try to avoid having too many inodes on each OST, while keeping
+ enough margin to allow for future usage of smaller files. This helps
+ reduce the format and e2fsck time and makes more space available for data.
+ </para>
<para>The table below shows the default
<emphasis role="italic">bytes-per-inode</emphasis> ratio ("inode ratio")
used for OSTs of various sizes when they are formatted.</para>
<screen>[oss#] mkfs.lustre --ost --mkfsoptions="-i $((8192 * 1024))" ...</screen>
</para>
<note>
- <para>OSTs formatted with ldiskfs are limited to a maximum of
- 320 million to 1 billion objects. Specifying a very small
- bytes-per-inode ratio for a large OST that causes this limit to be
- exceeded can cause either premature out-of-space errors and prevent
+ <para>OSTs formatted with ldiskfs can use a maximum of approximately
+ 320 million objects per MDT, up to a maximum of 4 billion inodes.
+ Specifying a very small bytes-per-inode ratio for a large OST that
+ exceeds this limit can cause either premature out-of-space errors and prevent
the full OST space from being used, or will waste space and slow down
e2fsck more than necessary. The default inode ratios are chosen to
ensure that the total number of inodes remain below this limit.
allocated blocks on the disk, disk speed, CPU speed, and the amount
of RAM on the server. Reasonable file system check times for valid
filesystems are 5-30 minutes per TiB, but may increase significantly
- if substantial errors are detected and need to be required.</para>
+ if substantial errors are detected and need to be repaired.</para>
</note>
- <para>For more details about formatting MDT and OST file systems,
+ <para>For further details about optimizing MDT and OST file systems,
see <xref linkend="dbdoclet.ldiskfs_raid_opts"/>.</para>
</section>
</section>
maximum of 1 MDT per file system, but a single MDS can host
multiple MDTs, each one for a separate file system.</para>
<para condition="l24">The Lustre software release 2.4 and later
- requires one MDT for the filesystem root. At least 255 more
+ requires one MDT for the filesystem root. Up to 255 more
MDTs can be added to the filesystem and attached into
the namespace with DNE remote or striped directories.</para>
</entry>
<para>Maximum OST size</para>
</entry>
<entry>
- <para>256TiB (ldiskfs), 256TiB (ZFS)</para>
+ <para>512TiB (ldiskfs), 512TiB (ZFS)</para>
</entry>
<entry>
<para>This is not a <emphasis>hard</emphasis> limit. Larger
typically go beyond the stated limit per OST because Lustre
can add capacity and performance with additional OSTs, and
having more OSTs improves aggregate I/O performance,
- minimizes contention, and allows parallel recovery (e2fsck).
+ minimizes contention, and allows parallel recovery (e2fsck
+ for ldiskfs OSTs, scrub for ZFS OSTs).
</para>
<para>
With 32-bit kernels, due to page cache limits, 16TB is the
<entry>
<para>The maximum number of clients is a constant that can
be changed at compile time. Up to 30000 clients have been
- used in production.</para>
+ used in production accessing a single filesystem.</para>
</entry>
</row>
<row>
<para>64 KiB</para>
</entry>
<entry>
- <para>Due to the 64 KiB PAGE_SIZE on some 64-bit machines,
- the minimum stripe size is set to 64 KiB.</para>
+ <para>Due to the use of 64 KiB PAGE_SIZE on some CPU
+ architectures such as ARM and POWER, the minimum stripe
+ size is 64 KiB so that a single page is not split over
+ multiple servers.</para>
</entry>
</row>
<row>
<entry>
- <para>Maximum object size</para>
+ <para>Maximum single object size</para>
</entry>
<entry>
<para>16TiB (ldiskfs), 256TiB (ZFS)</para>
32-bit systems imposed by the kernel memory subsystem. On
64-bit systems this limit does not exist. Hence, files can
be 2^63 bits (8EiB) in size if the backing filesystem can
- support large enough objects.</para>
+ support large enough objects and/or the files are sparse.</para>
<para>A single file can have a maximum of 2000 stripes, which
- gives an upper single file limit of 31.25 PiB for 64-bit
+ gives an upper single file data capacity of 31.25 PiB for 64-bit
ldiskfs systems. The actual amount of data that can be stored
in a file depends upon the amount of free space in each OST
on which the file is striped.</para>
</entry>
<entry>
<para>4 billion (ldiskfs), 256 trillion (ZFS)</para>
- <para condition='l24'>up to 256 times the per-MDT limit</para>
+ <para condition='l24'>this is a per-MDT limit</para>
</entry>
<entry>
<para>The ldiskfs filesystem imposes an upper limit of
of open files, but the practical limit depends on the amount of
RAM on the MDS. No "tables" for open files exist on the
MDS, as they are only linked in a list to a given client's
- export. Each client process probably has a limit of several
- thousands of open files which depends on the ulimit.</para>
+ export. Each client process has a limit of several
+ thousands of open files which depends on its ulimit.</para>
</entry>
</row>
</tbody>
<para>Load placed on server</para>
</listitem>
</itemizedlist>
- <para>The amount of memory used by the MDS is a function of how many clients are on the system, and how many files they are using in their working set. This is driven, primarily, by the number of locks a client can hold at one time. The number of locks held by clients varies by load and memory availability on the server. Interactive clients can hold in excess of 10,000 locks at times. On the MDS, memory usage is approximately 2 KB per file, including the Lustre distributed lock manager (DLM) lock and kernel data structures for the files currently in use. Having file data in cache can improve metadata performance by a factor of 10x or more compared to reading it from disk.</para>
+ <para>The amount of memory used by the MDS is a function of how many clients are on
+ the system, and how many files they are using in their working set. This is driven,
+ primarily, by the number of locks a client can hold at one time. The number of locks
+ held by clients varies by load and memory availability on the server. Interactive
+ clients can hold in excess of 10,000 locks at times. On the MDS, memory usage is
+ approximately 2 KB per file, including the Lustre distributed lock manager (LDLM)
+ lock and kernel data structures for the files currently in use. Having file data
+ in cache can improve metadata performance by a factor of 10x or more compared to
+ reading it from storage.</para>
<para>MDS memory requirements include:</para>
<itemizedlist>
<listitem>
- <para><emphasis role="bold">File system metadata</emphasis> : A reasonable amount of RAM needs to be available for file system metadata. While no hard limit can be placed on the amount of file system metadata, if more RAM is available, then the disk I/O is needed less often to retrieve the metadata.</para>
+ <para><emphasis role="bold">File system metadata</emphasis>:
+ A reasonable amount of RAM needs to be available for file system metadata.
+ While no hard limit can be placed on the amount of file system metadata,
+ if more RAM is available, then the disk I/O is needed less often to retrieve
+ the metadata.</para>
</listitem>
<listitem>
- <para><emphasis role="bold">Network transport</emphasis> : If you are using TCP or other network transport that uses system memory for send/receive buffers, this memory requirement must also be taken into consideration.</para>
+ <para><emphasis role="bold">Network transport</emphasis>:
+ If you are using TCP or other network transport that uses system memory for
+ send/receive buffers, this memory requirement must also be taken into
+ consideration.</para>
</listitem>
<listitem>
- <para><emphasis role="bold">Journal size</emphasis> : By default, the journal size is 400 MB for each Lustre ldiskfs file system. This can pin up to an equal amount of RAM on the MDS node per file system.</para>
+ <para><emphasis role="bold">Journal size</emphasis>:
+ By default, the journal size is 4096 MB for each MDT ldiskfs file system.
+ This can pin up to an equal amount of RAM on the MDS node per file system.</para>
</listitem>
<listitem>
- <para><emphasis role="bold">Failover configuration</emphasis> : If the MDS node will be used for failover from another node, then the RAM for each journal should be doubled, so the backup server can handle the additional load if the primary server fails.</para>
+ <para><emphasis role="bold">Failover configuration</emphasis>:
+ If the MDS node will be used for failover from another node, then the RAM
+ for each journal should be doubled, so the backup server can handle the
+ additional load if the primary server fails.</para>
</listitem>
</itemizedlist>
<section remap="h4">
<title><indexterm><primary>setup</primary><secondary>memory</secondary><tertiary>MDS</tertiary></indexterm>Calculating MDS Memory Requirements</title>
- <para>By default, 400 MB are used for the file system journal. Additional RAM is used for caching file data for the larger working set, which is not actively in use by clients but should be kept "hot" for improved access times. Approximately 1.5 KB per file is needed to keep a file in cache without a lock.</para>
- <para>For example, for a single MDT on an MDS with 1,000 clients, 16 interactive nodes, and a 2 million file working set (of which 400,000 files are cached on the clients):</para>
+ <para>By default, 4096 MB are used for the ldiskfs filesystem journal. Additional
+ RAM is used for caching file data for the larger working set, which is not
+ actively in use by clients but should be kept "hot" for improved
+ access times. Approximately 1.5 KB per file is needed to keep a file in cache
+ without a lock.</para>
+ <para>For example, for a single MDT on an MDS with 1,024 clients, 12 interactive
+ login nodes, and a 6 million file working set (of which 4M files are cached
+ on the clients):</para>
<informalexample>
- <para>Operating system overhead = 512 MB</para>
- <para>File system journal = 400 MB</para>
- <para>1000 * 4-core clients * 100 files/core * 2kB = 800 MB</para>
- <para>16 interactive clients * 10,000 files * 2kB = 320 MB</para>
- <para>1,600,000 file extra working set * 1.5kB/file = 2400 MB</para>
+ <para>Operating system overhead = 1024 MB</para>
+ <para>File system journal = 4096 MB</para>
+ <para>1024 * 4-core clients * 1024 files/core * 2kB = 4096 MB</para>
+ <para>12 interactive clients * 100,000 files * 2kB = 2400 MB</para>
+ <para>2M file extra working set * 1.5kB/file = 3096 MB</para>
</informalexample>
- <para>Thus, the minimum requirement for a system with this configuration is at least 4 GB of RAM. However, additional memory may significantly improve performance.</para>
- <para>For directories containing 1 million or more files, more memory may provide a significant benefit. For example, in an environment where clients randomly access one of 10 million files, having extra memory for the cache significantly improves performance.</para>
+ <para>Thus, the minimum requirement for an MDT with this configuration is at least
+ 16 GB of RAM. Additional memory may significantly improve performance.</para>
+ <para>For directories containing 1 million or more files, more memory can provide
+ a significant benefit. For example, in an environment where clients randomly
+ access one of 10 million files, having extra memory for the cache significantly
+ improves performance.</para>
</section>
</section>
<section remap="h3">
<title><indexterm><primary>setup</primary><secondary>memory</secondary><tertiary>OSS</tertiary></indexterm>OSS Memory Requirements</title>
- <para>When planning the hardware for an OSS node, consider the memory usage of several
- components in the Lustre file system (i.e., journal, service threads, file system metadata,
- etc.). Also, consider the effect of the OSS read cache feature, which consumes memory as it
- caches data on the OSS node.</para>
- <para>In addition to the MDS memory requirements mentioned in <xref linkend="dbdoclet.50438256_87676"/>, the OSS requirements include:</para>
+ <para>When planning the hardware for an OSS node, consider the memory usage of
+ several components in the Lustre file system (i.e., journal, service threads,
+ file system metadata, etc.). Also, consider the effect of the OSS read cache
+ feature, which consumes memory as it caches data on the OSS node.</para>
+ <para>In addition to the MDS memory requirements mentioned above,
+ the OSS requirements also include:</para>
<itemizedlist>
<listitem>
- <para><emphasis role="bold">Service threads</emphasis> : The service threads on the OSS node pre-allocate a 4 MB I/O buffer for each ost_io service thread, so these buffers do not need to be allocated and freed for each I/O request.</para>
+ <para><emphasis role="bold">Service threads</emphasis>:
+ The service threads on the OSS node pre-allocate an RPC-sized MB I/O buffer
+ for each ost_io service thread, so these buffers do not need to be allocated
+ and freed for each I/O request.</para>
</listitem>
<listitem>
- <para><emphasis role="bold">OSS read cache</emphasis> : OSS read cache provides read-only
- caching of data on an OSS, using the regular Linux page cache to store the data. Just
- like caching from a regular file system in the Linux operating system, OSS read cache
- uses as much physical memory as is available.</para>
+ <para><emphasis role="bold">OSS read cache</emphasis>:
+ OSS read cache provides read-only caching of data on an OSS, using the regular
+ Linux page cache to store the data. Just like caching from a regular file
+ system in the Linux operating system, OSS read cache uses as much physical
+ memory as is available.</para>
</listitem>
</itemizedlist>
- <para>The same calculation applies to files accessed from the OSS as for the MDS, but the load is distributed over many more OSSs nodes, so the amount of memory required for locks, inode cache, etc. listed under MDS is spread out over the OSS nodes.</para>
- <para>Because of these memory requirements, the following calculations should be taken as determining the absolute minimum RAM required in an OSS node.</para>
+ <para>The same calculation applies to files accessed from the OSS as for the MDS,
+ but the load is distributed over many more OSSs nodes, so the amount of memory
+ required for locks, inode cache, etc. listed under MDS is spread out over the
+ OSS nodes.</para>
+ <para>Because of these memory requirements, the following calculations should be
+ taken as determining the absolute minimum RAM required in an OSS node.</para>
<section remap="h4">
<title><indexterm><primary>setup</primary><secondary>memory</secondary><tertiary>OSS</tertiary></indexterm>Calculating OSS Memory Requirements</title>
- <para>The minimum recommended RAM size for an OSS with two OSTs is computed below:</para>
+ <para>The minimum recommended RAM size for an OSS with eight OSTs is:</para>
<informalexample>
- <para>Ethernet/TCP send/receive buffers (4 MB * 512 threads) = 2048 MB</para>
- <para>400 MB journal size * 2 OST devices = 800 MB</para>
- <para>1.5 MB read/write per OST IO thread * 512 threads = 768 MB</para>
- <para>600 MB file system read cache * 2 OSTs = 1200 MB</para>
- <para>1000 * 4-core clients * 100 files/core * 2kB = 800MB</para>
- <para>16 interactive clients * 10,000 files * 2kB = 320MB</para>
- <para>1,600,000 file extra working set * 1.5kB/file = 2400MB</para>
- <para> DLM locks + file system metadata TOTAL = 3520MB</para>
- <para>Per OSS DLM locks + file system metadata = 3520MB/6 OSS = 600MB (approx.)</para>
- <para>Per OSS RAM minimum requirement = 4096MB (approx.)</para>
+ <para>Linux kernel and userspace daemon memory = 1024 MB</para>
+ <para>Network send/receive buffers (16 MB * 512 threads) = 8192 MB</para>
+ <para>1024 MB ldiskfs journal size * 8 OST devices = 8192 MB</para>
+ <para>16 MB read/write buffer per OST IO thread * 512 threads = 8192 MB</para>
+ <para>2048 MB file system read cache * 8 OSTs = 16384 MB</para>
+ <para>1024 * 4-core clients * 1024 files/core * 2kB/file = 8192 MB</para>
+ <para>12 interactive clients * 100,000 files * 2kB/file = 2400 MB</para>
+ <para>2M file extra working set * 2kB/file = 4096 MB</para>
+ <para>DLM locks + file cache TOTAL = 31072 MB</para>
+ <para>Per OSS DLM locks + file system metadata = 31072 MB/4 OSS = 7768 MB (approx.)</para>
+ <para>Per OSS RAM minimum requirement = 32 GB (approx.)</para>
</informalexample>
- <para>This consumes about 1,400 MB just for the pre-allocated buffers, and an additional 2 GB for minimal file system and kernel usage. Therefore, for a non-failover configuration, the minimum RAM would be 4 GB for an OSS node with two OSTs. Adding additional memory on the OSS will improve the performance of reading smaller, frequently-accessed files.</para>
- <para>For a failover configuration, the minimum RAM would be at least 6 GB. For 4 OSTs on each OSS in a failover configuration 10GB of RAM is reasonable. When the OSS is not handling any failed-over OSTs the extra RAM will be used as a read cache.</para>
- <para>As a reasonable rule of thumb, about 2 GB of base memory plus 1 GB per OST can be used. In failover configurations, about 2 GB per OST is needed.</para>
+ <para>This consumes about 16 GB just for pre-allocated buffers, and an
+ additional 1 GB for minimal file system and kernel usage. Therefore, for a
+ non-failover configuration, the minimum RAM would be about 32 GB for an OSS node
+ with eight OSTs. Adding additional memory on the OSS will improve the performance
+ of reading smaller, frequently-accessed files.</para>
+ <para>For a failover configuration, the minimum RAM would be at least 48 GB,
+ as some of the memory is per-node. When the OSS is not handling any failed-over
+ OSTs the extra RAM will be used as a read cache.</para>
+ <para>As a reasonable rule of thumb, about 8 GB of base memory plus 3 GB per OST
+ can be used. In failover configurations, about 6 GB per OST is needed.</para>
</section>
</section>
</section>
git://git.whamcloud.com / doc / manual.git / blobdiff