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"
4 xml:id="backupandrestore">
5 <title xml:id="backupandrestore.title">Backing Up and Restoring a File
7 <para>This chapter describes how to backup and restore at the file
8 system-level, device-level and file-level in a Lustre file system. Each
9 backup approach is described in the the following sections:</para>
13 <xref linkend="dbdoclet.backup_file"/>
18 <xref linkend="dbdoclet.backup_device"/>
23 <xref linkend="backup_fs_level"/>
28 <xref linkend="backup_fs_level.restore"/>
33 <xref linkend="dbdoclet.backup_lvm_snapshot"/>
37 <para>It is <emphasis>strongly</emphasis> recommended that sites perform
38 periodic device-level backup of the MDT(s)
39 (<xref linkend="dbdoclet.backup_device"/>),
40 for example twice a week with alternate backups going to a separate
41 device, even if there is not enough capacity to do a full backup of all
42 of the filesystem data. Even if there are separate file-level backups of
43 some or all files in the filesystem, having a device-level backup of the
44 MDT can be very useful in case of MDT failure or corruption. Being able to
45 restore a device-level MDT backup can avoid the significantly longer process
46 of restoring the entire filesystem from backup. Since the MDT is required
47 for access to all files, its loss would otherwise force full restore of the
48 filesystem (if that is even possible) even if the OSTs are still OK.</para>
49 <para>Performing a periodic device-level MDT backup can be done relatively
50 inexpensively because the storage need only be connected to the primary
51 MDS (it can be manually connected to the backup MDS in the rare case
52 it is needed), and only needs good linear read/write performance. While
53 the device-level MDT backup is not useful for restoring individual files,
54 it is most efficient to handle the case of MDT failure or corruption.</para>
55 <section xml:id="dbdoclet.backup_file">
58 <primary>backup</primary>
61 <primary>restoring</primary>
65 <primary>LVM</primary>
69 <primary>rsync</primary>
71 </indexterm>Backing up a File System</title>
72 <para>Backing up a complete file system gives you full control over the
73 files to back up, and allows restoration of individual files as needed.
74 File system-level backups are also the easiest to integrate into existing
75 backup solutions.</para>
76 <para>File system backups are performed from a Lustre client (or many
77 clients working parallel in different directories) rather than on
78 individual server nodes; this is no different than backing up any other
80 <para>However, due to the large size of most Lustre file systems, it is
81 not always possible to get a complete backup. We recommend that you back
82 up subsets of a file system. This includes subdirectories of the entire
83 file system, filesets for a single user, files incremented by date, and
84 so on, so that restores can be done more efficiently.</para>
86 <para>Lustre internally uses a 128-bit file identifier (FID) for all
87 files. To interface with user applications, the 64-bit inode numbers
88 are returned by the <literal>stat()</literal>,
89 <literal>fstat()</literal>, and
90 <literal>readdir()</literal> system calls on 64-bit applications, and
91 32-bit inode numbers to 32-bit applications.</para>
92 <para>Some 32-bit applications accessing Lustre file systems (on both
93 32-bit and 64-bit CPUs) may experience problems with the
94 <literal>stat()</literal>,
95 <literal>fstat()</literal> or
96 <literal>readdir()</literal> system calls under certain circumstances,
97 though the Lustre client should return 32-bit inode numbers to these
99 <para>In particular, if the Lustre file system is exported from a 64-bit
100 client via NFS to a 32-bit client, the Linux NFS server will export
101 64-bit inode numbers to applications running on the NFS client. If the
102 32-bit applications are not compiled with Large File Support (LFS), then
104 <literal>EOVERFLOW</literal> errors when accessing the Lustre files. To
105 avoid this problem, Linux NFS clients can use the kernel command-line
106 option "<literal>nfs.enable_ino64=0</literal>" in order to force the
107 NFS client to export 32-bit inode numbers to the client.</para>
109 <emphasis role="bold">Workaround</emphasis>: We very strongly recommend
111 <literal>tar(1)</literal> and other utilities that depend on the inode
112 number to uniquely identify an inode to be run on 64-bit clients. The
113 128-bit Lustre file identifiers cannot be uniquely mapped to a 32-bit
114 inode number, and as a result these utilities may operate incorrectly on
115 32-bit clients. While there is still a small chance of inode number
116 collisions with 64-bit inodes, the FID allocation pattern is designed
117 to avoid collisions for long periods of usage.</para>
122 <primary>backup</primary>
123 <secondary>rsync</secondary>
124 </indexterm>Lustre_rsync</title>
126 <literal>lustre_rsync</literal> feature keeps the entire file system in
127 sync on a backup by replicating the file system's changes to a second
128 file system (the second file system need not be a Lustre file system, but
129 it must be sufficiently large).
130 <literal>lustre_rsync</literal> uses Lustre changelogs to efficiently
131 synchronize the file systems without having to scan (directory walk) the
132 Lustre file system. This efficiency is critically important for large
133 file systems, and distinguishes the Lustre
134 <literal>lustre_rsync</literal> feature from other replication/backup
139 <primary>backup</primary>
140 <secondary>rsync</secondary>
141 <tertiary>using</tertiary>
142 </indexterm>Using Lustre_rsync</title>
144 <literal>lustre_rsync</literal> feature works by periodically running
145 <literal>lustre_rsync</literal>, a userspace program used to
146 synchronize changes in the Lustre file system onto the target file
148 <literal>lustre_rsync</literal> utility keeps a status file, which
149 enables it to be safely interrupted and restarted without losing
150 synchronization between the file systems.</para>
151 <para>The first time that
152 <literal>lustre_rsync</literal> is run, the user must specify a set of
153 parameters for the program to use. These parameters are described in
154 the following table and in
155 <xref linkend="dbdoclet.lustre_rsync" />. On subsequent runs, these
156 parameters are stored in the the status file, and only the name of the
157 status file needs to be passed to
158 <literal>lustre_rsync</literal>.</para>
160 <literal>lustre_rsync</literal>:</para>
163 <para>Register the changelog user. For details, see the
164 <xref linkend="systemconfigurationutilities" />(
165 <literal>changelog_register</literal>) parameter in the
166 <xref linkend="systemconfigurationutilities" />(
167 <literal>lctl</literal>).</para>
173 <para>Verify that the Lustre file system (source) and the replica
174 file system (target) are identical
175 <emphasis>before</emphasis> registering the changelog user. If the
176 file systems are discrepant, use a utility, e.g. regular
177 <literal>rsync</literal>(not
178 <literal>lustre_rsync</literal>), to make them identical.</para>
182 <literal>lustre_rsync</literal> utility uses the following
184 <informaltable frame="all">
186 <colspec colname="c1" colwidth="3*" />
187 <colspec colname="c2" colwidth="10*" />
192 <emphasis role="bold">Parameter</emphasis>
197 <emphasis role="bold">Description</emphasis>
207 <replaceable>src</replaceable></literal>
211 <para>The path to the root of the Lustre file system (source)
212 which will be synchronized. This is a mandatory option if a
213 valid status log created during a previous synchronization
215 <literal>--statuslog</literal>) is not specified.</para>
222 <replaceable>tgt</replaceable></literal>
226 <para>The path to the root where the source file system will
227 be synchronized (target). This is a mandatory option if the
228 status log created during a previous synchronization
230 <literal>--statuslog</literal>) is not specified. This option
231 can be repeated if multiple synchronization targets are
239 <replaceable>mdt</replaceable></literal>
243 <para>The metadata device to be synchronized. A changelog
244 user must be registered for this device. This is a mandatory
245 option if a valid status log created during a previous
246 synchronization operation (
247 <literal>--statuslog</literal>) is not specified.</para>
254 <replaceable>userid</replaceable></literal>
258 <para>The changelog user ID for the specified MDT. To use
259 <literal>lustre_rsync</literal>, the changelog user must be
260 registered. For details, see the
261 <literal>changelog_register</literal> parameter in
262 <xref linkend="systemconfigurationutilities" />(
263 <literal>lctl</literal>). This is a mandatory option if a
264 valid status log created during a previous synchronization
266 <literal>--statuslog</literal>) is not specified.</para>
272 <literal>--statuslog=
273 <replaceable>log</replaceable></literal>
277 <para>A log file to which synchronization status is saved.
279 <literal>lustre_rsync</literal> utility starts, if the status
280 log from a previous synchronization operation is specified,
281 then the state is read from the log and otherwise mandatory
282 <literal>--source</literal>,
283 <literal>--target</literal> and
284 <literal>--mdt</literal> options can be skipped. Specifying
286 <literal>--source</literal>,
287 <literal>--target</literal> and/or
288 <literal>--mdt</literal> options, in addition to the
289 <literal>--statuslog</literal> option, causes the specified
290 parameters in the status log to be overridden. Command line
291 options take precedence over options in the status
298 <replaceable>yes|no</replaceable></literal>
301 <para>Specifies whether extended attributes (
302 <literal>xattrs</literal>) are synchronized or not. The
303 default is to synchronize extended attributes.</para>
306 <para>Disabling xattrs causes Lustre striping information
307 not to be synchronized.</para>
315 <literal>--verbose</literal>
319 <para>Produces verbose output.</para>
325 <literal>--dry-run</literal>
329 <para>Shows the output of
330 <literal>lustre_rsync</literal> commands (
331 <literal>copy</literal>,
332 <literal>mkdir</literal>, etc.) on the target file system
333 without actually executing them.</para>
339 <literal>--abort-on-err</literal>
343 <para>Stops processing the
344 <literal>lustre_rsync</literal> operation if an error occurs.
345 The default is to continue the operation.</para>
355 <primary>backup</primary>
356 <secondary>rsync</secondary>
357 <tertiary>examples</tertiary>
359 <literal>lustre_rsync</literal> Examples</title>
361 <literal>lustre_rsync</literal> commands are listed below.</para>
362 <para>Register a changelog user for an MDT (e.g.
363 <literal>testfs-MDT0000</literal>).</para>
364 <screen># lctl --device testfs-MDT0000 changelog_register testfs-MDT0000
365 Registered changelog userid 'cl1'</screen>
366 <para>Synchronize a Lustre file system (
367 <literal>/mnt/lustre</literal>) to a target file system (
368 <literal>/mnt/target</literal>).</para>
369 <screen>$ lustre_rsync --source=/mnt/lustre --target=/mnt/target \
370 --mdt=testfs-MDT0000 --user=cl1 --statuslog sync.log --verbose
371 Lustre filesystem: testfs
372 MDT device: testfs-MDT0000
376 Changelog registration: cl1
377 Starting changelog record: 0
379 lustre_rsync took 1 seconds
380 Changelog records consumed: 22</screen>
381 <para>After the file system undergoes changes, synchronize the changes
382 onto the target file system. Only the
383 <literal>statuslog</literal> name needs to be specified, as it has all
384 the parameters passed earlier.</para>
385 <screen>$ lustre_rsync --statuslog sync.log --verbose
386 Replicating Lustre filesystem: testfs
387 MDT device: testfs-MDT0000
391 Changelog registration: cl1
392 Starting changelog record: 22
394 lustre_rsync took 2 seconds
395 Changelog records consumed: 42</screen>
396 <para>To synchronize a Lustre file system (
397 <literal>/mnt/lustre</literal>) to two target file systems (
398 <literal>/mnt/target1</literal> and
399 <literal>/mnt/target2</literal>).</para>
400 <screen>$ lustre_rsync --source=/mnt/lustre --target=/mnt/target1 \
401 --target=/mnt/target2 --mdt=testfs-MDT0000 --user=cl1 \
402 --statuslog sync.log</screen>
406 <section xml:id="dbdoclet.backup_device">
409 <primary>backup</primary>
410 <secondary>MDT/OST device level</secondary>
411 </indexterm>Backing Up and Restoring an MDT or OST (ldiskfs Device Level)</title>
412 <para>In some cases, it is useful to do a full device-level backup of an
413 individual device (MDT or OST), before replacing hardware, performing
414 maintenance, etc. Doing full device-level backups ensures that all of the
415 data and configuration files is preserved in the original state and is the
416 easiest method of doing a backup. For the MDT file system, it may also be
417 the fastest way to perform the backup and restore, since it can do large
418 streaming read and write operations at the maximum bandwidth of the
419 underlying devices.</para>
421 <para>Keeping an updated full backup of the MDT is especially important
422 because permanent failure or corruption of the MDT file system renders
423 the much larger amount of data in all the OSTs largely inaccessible and
424 unusable. The storage needed for one or two full MDT device backups
425 is much smaller than doing a full filesystem backup, and can use less
426 expensive storage than the actual MDT device(s) since it only needs to
427 have good streaming read/write speed instead of high random IOPS.</para>
429 <para>If hardware replacement is the reason for the backup or if a spare
430 storage device is available, it is possible to do a raw copy of the MDT or
431 OST from one block device to the other, as long as the new device is at
432 least as large as the original device. To do this, run:</para>
433 <screen>dd if=/dev/{original} of=/dev/{newdev} bs=4M</screen>
434 <para>If hardware errors cause read problems on the original device, use
435 the command below to allow as much data as possible to be read from the
436 original device while skipping sections of the disk with errors:</para>
437 <screen>dd if=/dev/{original} of=/dev/{newdev} bs=4k conv=sync,noerror /
438 count={original size in 4kB blocks}</screen>
439 <para>Even in the face of hardware errors, the <literal>ldiskfs</literal>
440 file system is very robust and it may be possible
441 to recover the file system data after running
442 <literal>e2fsck -fy /dev/{newdev}</literal> on the new device.</para>
443 <para>With Lustre software version 2.6 and later, the
444 <literal>LFSCK</literal> scanning will automatically move objects from
445 <literal>lost+found</literal> back into its correct location on the OST
446 after directory corruption.</para>
447 <para>In order to ensure that the backup is fully consistent, the MDT or
448 OST must be unmounted, so that there are no changes being made to the
449 device while the data is being transferred. If the reason for the
450 backup is preventative (i.e. MDT backup on a running MDS in case of
451 future failures) then it is possible to perform a consistent backup from
452 an LVM snapshot. If an LVM snapshot is not available, and taking the
453 MDS offline for a backup is unacceptable, it is also possible to perform
454 a backup from the raw MDT block device. While the backup from the raw
455 device will not be fully consistent due to ongoing changes, the vast
456 majority of ldiskfs metadata is statically allocated, and inconsistencies
457 in the backup can be fixed by running <literal>e2fsck</literal> on the
458 backup device, and is still much better than not having any backup at all.
461 <section xml:id="backup_fs_level">
464 <primary>backup</primary>
465 <secondary>OST file system</secondary>
468 <primary>backup</primary>
469 <secondary>MDT file system</secondary>
470 </indexterm>Backing Up an OST or MDT (Backend File System Level)</title>
471 <para>This procedure provides an alternative to backup or migrate the data
472 of an OST or MDT at the file level. At the file-level, unused space is
473 omitted from the backup and the process may be completed quicker with a
474 smaller total backup size. Backing up a single OST device is not
475 necessarily the best way to perform backups of the Lustre file system,
476 since the files stored in the backup are not usable without metadata stored
477 on the MDT and additional file stripes that may be on other OSTs. However,
478 it is the preferred method for migration of OST devices, especially when it
479 is desirable to reformat the underlying file system with different
480 configuration options or to reduce fragmentation.</para>
482 <para>Since Lustre stores internal metadata that maps FIDs to local
483 inode numbers via the Object Index file, they need to be rebuilt at
484 first mount after a restore is detected so that file-level MDT backup
485 and restore is supported. The OI Scrub rebuilds these automatically
486 at first mount after a restore is detected, which may affect MDT
487 performance after mount until the rebuild is completed. Progress can
488 be monitored via <literal>lctl get_param osd-*.*.oi_scrub</literal>
489 on the MDS or OSS node where the target filesystem was restored.
492 <section xml:id="backup_fs_level.index_objects" condition="l2B">
495 <primary>backup</primary>
496 <secondary>index objects</secondary>
497 </indexterm>Backing Up an OST or MDT (Backend File System Level)</title>
498 <para>Prior to Lustre software release 2.11.0, we can only do the backend
499 file system level backup and restore process for ldiskfs-based systems.
500 The ability to perform a zfs-based MDT/OST file system level backup and
501 restore is introduced beginning in Lustre software release 2.11.0.
502 Differing from an ldiskfs-based system, index objects must be backed up
503 before the unmount of the target (MDT or OST) in order to be able to
504 restore the file system successfully. To enable index backup on the
505 target, execute the following command on the target server:</para>
506 <screen># lctl set_param osd-*.${fsname}-${target}.index_backup=1</screen>
507 <para><replaceable>${target}</replaceable> is composed of the target type
508 (MDT or OST) plus the target index, such as <literal>MDT0000</literal>,
509 <literal>OST0001</literal>, and so on.</para>
510 <note><para>The index_backup is also valid for an ldiskfs-based system,
511 that will be used when migrating data between ldiskfs-based and
512 zfs-based systems as described in <xref linkend="migrate_backends"/>.
515 <section xml:id="backup_fs_level.ost_mdt">
518 <primary>backup</primary>
519 <secondary>OST and MDT</secondary>
520 </indexterm>Backing Up an OST or MDT</title>
521 <para>The below examples show backing up an OST filesystem. When backing
522 up an MDT, substitute <literal>mdt</literal> for <literal>ost</literal>
523 in the instructions below.</para>
526 <para><emphasis role="bold">Umount the target</emphasis></para>
529 <para><emphasis role="bold">Make a mountpoint for the file system.
531 <screen>[oss]# mkdir -p /mnt/ost</screen>
534 <para><emphasis role="bold">Mount the file system.</emphasis></para>
535 <para>For ldiskfs-based systems:</para>
536 <screen>[oss]# mount -t ldiskfs /dev/<emphasis>{ostdev}</emphasis> /mnt/ost</screen>
537 <para>For zfs-based systems:</para>
540 <para>Import the pool for the target if it is exported. For example:
541 <screen>[oss]# zpool import lustre-ost [-d ${ostdev_dir}]</screen>
545 <para>Enable the <literal>canmount</literal> property on the target
546 filesystem. For example:
547 <screen>[oss]# zfs set canmount=on ${fsname}-ost/ost</screen>
548 You also can specify the mountpoint property. By default, it will
549 be: <literal>/${fsname}-ost/ost</literal>
553 <para>Mount the target as 'zfs'. For example:
554 <screen>[oss]# zfs mount ${fsname}-ost/ost</screen>
561 <emphasis role="bold">Change to the mountpoint being backed
564 <screen>[oss]# cd /mnt/ost</screen>
568 <emphasis role="bold">Back up the extended attributes.</emphasis>
570 <screen>[oss]# getfattr -R -d -m '.*' -e hex -P . > ea-$(date +%Y%m%d).bak</screen>
572 <para>If the <literal>tar(1)</literal> command supports the
573 <literal>--xattr</literal> option (see below), the
574 <literal>getfattr</literal> step may be unnecessary as long as tar
575 correctly backs up the <literal>trusted.*</literal> attributes.
576 However, completing this step is not harmful and can serve as an
577 added safety measure.</para>
580 <para>In most distributions, the
581 <literal>getfattr</literal> command is part of the
582 <literal>attr</literal> package. If the
583 <literal>getfattr</literal> command returns errors like
584 <literal>Operation not supported</literal>, then the kernel does not
585 correctly support EAs. Stop and use a different backup method.</para>
590 <emphasis role="bold">Verify that the
591 <literal>ea-$date.bak</literal> file has properly backed up the EA
592 data on the OST.</emphasis>
594 <para>Without this attribute data, the MDT restore process will fail
595 and result in an unusable filesystem. The OST restore process may be
596 missing extra data that can be very useful in case of later file system
597 corruption. Look at this file with <literal>more</literal> or a text
598 editor. Each object file should have a corresponding item similar to
600 <screen>[oss]# file: O/0/d0/100992
602 0x0d822200000000004a8a73e500000000808a0100000000000000000000000000</screen>
606 <emphasis role="bold">Back up all file system data.</emphasis>
608 <screen>[oss]# tar czvf {backup file}.tgz [--xattrs] [--xattrs-include="trusted.*" --sparse .</screen>
611 <literal>--sparse</literal> option is vital for backing up an MDT.
612 Very old versions of tar may not support the
613 <literal>--sparse</literal> option correctly, which may cause the
614 MDT backup to take a long time. Known-working versions include
615 the tar from Red Hat Enterprise Linux distribution (RHEL version
616 6.3 or newer) or GNU tar version 1.25 and newer.</para>
619 <para>The tar <literal>--xattrs</literal> option is only available
620 in GNU tar version 1.27 or later or in RHEL 6.3 or newer. The
621 <literal>--xattrs-include="trusted.*"</literal> option is
622 <emphasis>required</emphasis> for correct restoration of the xattrs
623 when using GNU tar 1.27 or RHEL 7 and newer.</para>
628 <emphasis role="bold">Change directory out of the file
631 <screen>[oss]# cd -</screen>
635 <emphasis role="bold">Unmount the file system.</emphasis>
637 <screen>[oss]# umount /mnt/ost</screen>
639 <para>When restoring an OST backup on a different node as part of an
640 OST migration, you also have to change server NIDs and use the
641 <literal>--writeconf</literal> command to re-generate the
642 configuration logs. See
643 <xref linkend="lustremaintenance" />(Changing a Server NID).</para>
649 <section xml:id="backup_fs_level.restore">
652 <primary>backup</primary>
653 <secondary>restoring file system backup</secondary>
654 </indexterm>Restoring a File-Level Backup</title>
655 <para>To restore data from a file-level backup, you need to format the
656 device, restore the file data and then restore the EA data.</para>
659 <para>Format the new device.</para>
660 <screen>[oss]# mkfs.lustre --ost --index {<emphasis>OST index</emphasis>}
661 --replace --fstype=${fstype} {<emphasis>other options</emphasis>} /dev/<emphasis>{newdev}</emphasis></screen>
664 <para>Set the file system label (<emphasis role="bold">ldiskfs-based
665 systems only</emphasis>).</para>
666 <screen>[oss]# e2label {fsname}-OST{index in hex} /mnt/ost</screen>
669 <para>Mount the file system.</para>
670 <para>For ldiskfs-based systems:</para>
671 <screen>[oss]# mount -t ldiskfs /dev/<emphasis>{newdev}</emphasis> /mnt/ost</screen>
672 <para>For zfs-based systems:</para>
675 <para>Import the pool for the target if it is exported. For example:
677 <screen>[oss]# zpool import lustre-ost [-d ${ostdev_dir}]</screen>
680 <para>Enable the canmount property on the target filesystem. For
682 <screen>[oss]# zfs set canmount=on ${fsname}-ost/ost</screen>
683 <para>You also can specify the <literal>mountpoint</literal>
684 property. By default, it will be:
685 <literal>/${fsname}-ost/ost</literal></para>
688 <para>Mount the target as 'zfs'. For example:</para>
689 <screen>[oss]# zfs mount ${fsname}-ost/ost</screen>
694 <para>Change to the new file system mount point.</para>
695 <screen>[oss]# cd /mnt/ost</screen>
698 <para>Restore the file system backup.</para>
699 <screen>[oss]# tar xzvpf <emphasis>{backup file}</emphasis> [--xattrs] [--xattrs-include="trusted.*"] --sparse</screen>
701 <para>The tar <literal>--xattrs</literal> option is only available
702 in GNU tar version 1.27 or later or in RHEL 6.3 or newer. The
703 <literal>--xattrs-include="trusted.*"</literal> option is
704 <emphasis>required</emphasis> for correct restoration of the
705 MDT xattrs when using GNU tar 1.27 or RHEL 7 and newer. Otherwise,
706 the <literal>setfattr</literal> step below should be used.
711 <para>If not using a version of tar that supports direct xattr
712 backups, restore the file system extended attributes.</para>
713 <screen>[oss]# setfattr --restore=ea-${date}.bak</screen>
716 <literal>--xattrs</literal> option is supported by tar and specified
717 in the step above, this step is redundant.</para>
721 <para>Verify that the extended attributes were restored.</para>
722 <screen>[oss]# getfattr -d -m ".*" -e hex O/0/d0/100992 trusted.fid= \
723 0x0d822200000000004a8a73e500000000808a0100000000000000000000000000</screen>
726 <para>Remove old OI and LFSCK files.</para>
727 <screen>[oss]# rm -rf oi.16* lfsck_* LFSCK</screen>
730 <para>Remove old CATALOGS.</para>
731 <screen>[oss]# rm -f CATALOGS</screen>
733 <para>This is optional for the MDT side only. The CATALOGS record the
734 llog file handlers that are used for recovering cross-server updates.
735 Before OI scrub rebuilds the OI mappings for the llog files, the
736 related recovery will get a failure if it runs faster than the
737 background OI scrub. This will result in a failure of the whole mount
738 process. OI scrub is an online tool, therefore, a mount failure means
739 that the OI scrub will be stopped. Removing the old CATALOGS will
740 avoid this potential trouble. The side-effect of removing old
741 CATALOGS is that the recovery for related cross-server updates will
742 be aborted. However, this can be handled by LFSCK after the system
747 <para>Change directory out of the file system.</para>
748 <screen>[oss]# cd -</screen>
751 <para>Unmount the new file system.</para>
752 <screen>[oss]# umount /mnt/ost</screen>
753 <note><para>If the restored system has a different NID from the backup
754 system, please change the NID. For detail, please refer to
755 <xref linkend="lustremaint.changingservernid" />. For example:</para>
756 <screen>[oss]# mount -t lustre -o nosvc ${fsname}-ost/ost /mnt/ost
757 [oss]# lctl replace_nids ${fsname}-OSTxxxx $new_nids
758 [oss]# umount /mnt/ost</screen></note>
761 <para>Mount the target as <literal>lustre</literal>.</para>
762 <para>Usually, we will use the <literal>-o abort_recov</literal> option
763 to skip unnecessary recovery. For example:</para>
764 <screen>[oss]# mount -t lustre -o abort_recov #{fsname}-ost/ost /mnt/ost</screen>
765 <para>Lustre can detect the restore automatically when mounting the
766 target, and then trigger OI scrub to rebuild the OIs and index objects
767 asynchronously in the background. You can check the OI scrub status
768 with the following command:</para>
769 <screen>[oss]# lctl get_param -n osd-${fstype}.${fsname}-${target}.oi_scrub</screen>
772 <para>If the file system was used between the time the backup was made and
773 when it was restored, then the online <literal>LFSCK</literal> tool will
774 automatically be run to ensure the filesystem is coherent. If all of the
775 device filesystems were backed up at the same time after Lustre was
776 was stopped, this step is unnecessary. In either case, the filesystem
777 will be immediately although there may be I/O errors reading
778 from files that are present on the MDT but not the OSTs, and files that
779 were created after the MDT backup will not be accessible or visible. See
780 <xref linkend="dbdoclet.lfsckadmin" />for details on using LFSCK.</para>
782 <section xml:id="dbdoclet.backup_lvm_snapshot">
785 <primary>backup</primary>
786 <secondary>using LVM</secondary>
787 </indexterm>Using LVM Snapshots with the Lustre File System</title>
788 <para>If you want to perform disk-based backups (because, for example,
789 access to the backup system needs to be as fast as to the primary Lustre
790 file system), you can use the Linux LVM snapshot tool to maintain multiple,
791 incremental file system backups.</para>
792 <para>Because LVM snapshots cost CPU cycles as new files are written,
793 taking snapshots of the main Lustre file system will probably result in
794 unacceptable performance losses. You should create a new, backup Lustre
795 file system and periodically (e.g., nightly) back up new/changed files to
796 it. Periodic snapshots can be taken of this backup file system to create a
797 series of "full" backups.</para>
799 <para>Creating an LVM snapshot is not as reliable as making a separate
800 backup, because the LVM snapshot shares the same disks as the primary MDT
801 device, and depends on the primary MDT device for much of its data. If
802 the primary MDT device becomes corrupted, this may result in the snapshot
803 being corrupted.</para>
808 <primary>backup</primary>
809 <secondary>using LVM</secondary>
810 <tertiary>creating</tertiary>
811 </indexterm>Creating an LVM-based Backup File System</title>
812 <para>Use this procedure to create a backup Lustre file system for use
813 with the LVM snapshot mechanism.</para>
816 <para>Create LVM volumes for the MDT and OSTs.</para>
817 <para>Create LVM devices for your MDT and OST targets. Make sure not
818 to use the entire disk for the targets; save some room for the
819 snapshots. The snapshots start out as 0 size, but grow as you make
820 changes to the current file system. If you expect to change 20% of
821 the file system between backups, the most recent snapshot will be 20%
822 of the target size, the next older one will be 40%, etc. Here is an
824 <screen>cfs21:~# pvcreate /dev/sda1
825 Physical volume "/dev/sda1" successfully created
826 cfs21:~# vgcreate vgmain /dev/sda1
827 Volume group "vgmain" successfully created
828 cfs21:~# lvcreate -L200G -nMDT0 vgmain
829 Logical volume "MDT0" created
830 cfs21:~# lvcreate -L200G -nOST0 vgmain
831 Logical volume "OST0" created
833 ACTIVE '/dev/vgmain/MDT0' [200.00 GB] inherit
834 ACTIVE '/dev/vgmain/OST0' [200.00 GB] inherit</screen>
837 <para>Format the LVM volumes as Lustre targets.</para>
838 <para>In this example, the backup file system is called
839 <literal>main</literal> and designates the current, most up-to-date
841 <screen>cfs21:~# mkfs.lustre --fsname=main --mdt --index=0 /dev/vgmain/MDT0
842 No management node specified, adding MGS to this MDT.
849 (MDT MGS first_time update )
850 Persistent mount opts: errors=remount-ro,iopen_nopriv,user_xattr
852 checking for existing Lustre data
854 formatting backing filesystem ldiskfs on /dev/vgmain/MDT0
855 target name main-MDT0000
857 options -i 4096 -I 512 -q -O dir_index -F
858 mkfs_cmd = mkfs.ext2 -j -b 4096 -L main-MDT0000 -i 4096 -I 512 -q
859 -O dir_index -F /dev/vgmain/MDT0
860 Writing CONFIGS/mountdata
861 cfs21:~# mkfs.lustre --mgsnode=cfs21 --fsname=main --ost --index=0
869 (OST first_time update )
870 Persistent mount opts: errors=remount-ro,extents,mballoc
871 Parameters: mgsnode=192.168.0.21@tcp
872 checking for existing Lustre data
874 formatting backing filesystem ldiskfs on /dev/vgmain/OST0
875 target name main-OST0000
877 options -I 256 -q -O dir_index -F
878 mkfs_cmd = mkfs.ext2 -j -b 4096 -L lustre-OST0000 -J size=400 -I 256
879 -i 262144 -O extents,uninit_bg,dir_nlink,huge_file,flex_bg -G 256
880 -E resize=4290772992,lazy_journal_init, -F /dev/vgmain/OST0
881 Writing CONFIGS/mountdata
882 cfs21:~# mount -t lustre /dev/vgmain/MDT0 /mnt/mdt
883 cfs21:~# mount -t lustre /dev/vgmain/OST0 /mnt/ost
884 cfs21:~# mount -t lustre cfs21:/main /mnt/main
892 <primary>backup</primary>
893 <secondary>new/changed files</secondary>
894 </indexterm>Backing up New/Changed Files to the Backup File
896 <para>At periodic intervals e.g., nightly, back up new and changed files
897 to the LVM-based backup file system.</para>
898 <screen>cfs21:~# cp /etc/passwd /mnt/main
900 cfs21:~# cp /etc/fstab /mnt/main
902 cfs21:~# ls /mnt/main
903 fstab passwd</screen>
908 <primary>backup</primary>
909 <secondary>using LVM</secondary>
910 <tertiary>creating snapshots</tertiary>
911 </indexterm>Creating Snapshot Volumes</title>
912 <para>Whenever you want to make a "checkpoint" of the main Lustre file
913 system, create LVM snapshots of all target MDT and OSTs in the LVM-based
914 backup file system. You must decide the maximum size of a snapshot ahead
915 of time, although you can dynamically change this later. The size of a
916 daily snapshot is dependent on the amount of data changed daily in the
917 main Lustre file system. It is likely that a two-day old snapshot will be
918 twice as big as a one-day old snapshot.</para>
919 <para>You can create as many snapshots as you have room for in the volume
920 group. If necessary, you can dynamically add disks to the volume
922 <para>The snapshots of the target MDT and OSTs should be taken at the
923 same point in time. Make sure that the cronjob updating the backup file
924 system is not running, since that is the only thing writing to the disks.
925 Here is an example:</para>
926 <screen>cfs21:~# modprobe dm-snapshot
927 cfs21:~# lvcreate -L50M -s -n MDT0.b1 /dev/vgmain/MDT0
928 Rounding up size to full physical extent 52.00 MB
929 Logical volume "MDT0.b1" created
930 cfs21:~# lvcreate -L50M -s -n OST0.b1 /dev/vgmain/OST0
931 Rounding up size to full physical extent 52.00 MB
932 Logical volume "OST0.b1" created
934 <para>After the snapshots are taken, you can continue to back up
935 new/changed files to "main". The snapshots will not contain the new
937 <screen>cfs21:~# cp /etc/termcap /mnt/main
938 cfs21:~# ls /mnt/main
945 <primary>backup</primary>
946 <secondary>using LVM</secondary>
947 <tertiary>restoring</tertiary>
948 </indexterm>Restoring the File System From a Snapshot</title>
949 <para>Use this procedure to restore the file system from an LVM
953 <para>Rename the LVM snapshot.</para>
954 <para>Rename the file system snapshot from "main" to "back" so you
955 can mount it without unmounting "main". This is recommended, but not
957 <literal>--reformat</literal> flag to
958 <literal>tunefs.lustre</literal> to force the name change. For
960 <screen>cfs21:~# tunefs.lustre --reformat --fsname=back --writeconf /dev/vgmain/MDT0.b1
961 checking for existing Lustre data
963 Reading CONFIGS/mountdata
964 Read previous values:
971 Persistent mount opts: errors=remount-ro,iopen_nopriv,user_xattr
980 Persistent mount opts: errors=remount-ro,iopen_nopriv,user_xattr
982 Writing CONFIGS/mountdata
983 cfs21:~# tunefs.lustre --reformat --fsname=back --writeconf /dev/vgmain/OST0.b1
984 checking for existing Lustre data
986 Reading CONFIGS/mountdata
987 Read previous values:
994 Persistent mount opts: errors=remount-ro,extents,mballoc
995 Parameters: mgsnode=192.168.0.21@tcp
1003 Persistent mount opts: errors=remount-ro,extents,mballoc
1004 Parameters: mgsnode=192.168.0.21@tcp
1005 Writing CONFIGS/mountdata
1007 <para>When renaming a file system, we must also erase the last_rcvd
1008 file from the snapshots</para>
1009 <screen>cfs21:~# mount -t ldiskfs /dev/vgmain/MDT0.b1 /mnt/mdtback
1010 cfs21:~# rm /mnt/mdtback/last_rcvd
1011 cfs21:~# umount /mnt/mdtback
1012 cfs21:~# mount -t ldiskfs /dev/vgmain/OST0.b1 /mnt/ostback
1013 cfs21:~# rm /mnt/ostback/last_rcvd
1014 cfs21:~# umount /mnt/ostback</screen>
1017 <para>Mount the file system from the LVM snapshot. For
1019 <screen>cfs21:~# mount -t lustre /dev/vgmain/MDT0.b1 /mnt/mdtback
1020 cfs21:~# mount -t lustre /dev/vgmain/OST0.b1 /mnt/ostback
1021 cfs21:~# mount -t lustre cfs21:/back /mnt/back</screen>
1024 <para>Note the old directory contents, as of the snapshot time. For
1026 <screen>cfs21:~/cfs/b1_5/lustre/utils# ls /mnt/back
1032 <section remap="h3">
1035 <primary>backup</primary>
1036 <secondary>using LVM</secondary>
1037 <tertiary>deleting</tertiary>
1038 </indexterm>Deleting Old Snapshots</title>
1039 <para>To reclaim disk space, you can erase old snapshots as your backup
1040 policy dictates. Run:</para>
1041 <screen>lvremove /dev/vgmain/MDT0.b1</screen>
1043 <section remap="h3">
1046 <primary>backup</primary>
1047 <secondary>using LVM</secondary>
1048 <tertiary>resizing</tertiary>
1049 </indexterm>Changing Snapshot Volume Size</title>
1050 <para>You can also extend or shrink snapshot volumes if you find your
1051 daily deltas are smaller or larger than expected. Run:</para>
1052 <screen>lvextend -L10G /dev/vgmain/MDT0.b1</screen>
1054 <para>Extending snapshots seems to be broken in older LVM. It is
1055 working in LVM v2.02.01.</para>
1059 <section xml:id="migrate_backends" condition="l2B">
1062 <primary>backup</primary>
1063 <secondary>ZFS ZPL</secondary>
1064 </indexterm>Migration Between ZFS and ldiskfs Target Filesystems
1066 <para>Beginning with Lustre 2.11.0, it is possible to migrate between
1067 ZFS and ldiskfs backends. For migrating OSTs, it is best to use
1068 <literal>lfs find</literal>/<literal>lfs_migrate</literal> to empty out
1069 an OST while the filesystem is in use and then reformat it with the new
1070 fstype. For instructions on removing the OST, please see
1071 <xref linkend="lustremaint.remove_ost"/>.</para>
1072 <section remap="h3" xml:id="migrate_backends.zfs2ldiskfs">
1075 <primary>backup</primary>
1076 <secondary>ZFS to ldiskfs</secondary>
1077 </indexterm>Migrate from a ZFS to an ldiskfs based filesystem</title>
1078 <para>The first step of the process is to make a ZFS backend backup
1079 using <literal>tar</literal> as described in
1080 <xref linkend="backup_fs_level"/>.</para>
1081 <para>Next, restore the backup to an ldiskfs-based system as described
1082 in <xref linkend="backup_fs_level.restore"/>.</para>
1084 <section remap="h3" xml:id="migrate_backends.ldiskfs2zfs">
1087 <primary>backup</primary>
1088 <secondary>ZFS to ldiskfs</secondary>
1089 </indexterm>Migrate from an ldiskfs to a ZFS based filesystem</title>
1090 <para>The first step of the process is to make an ldiskfs backend backup
1091 using <literal>tar</literal> as described in
1092 <xref linkend="backup_fs_level"/>.</para>
1093 <para><emphasis role="strong">Caution:</emphasis>For a migration from
1094 ldiskfs to zfs, it is required to enable index_backup before the
1095 unmount of the target. This is an additional step for a regular
1096 ldiskfs-based backup/restore and easy to be missed.</para>
1097 <para>Next, restore the backup to an ldiskfs-based system as described
1098 in <xref linkend="backup_fs_level.restore"/>.</para>
1103 vim:expandtab:shiftwidth=2:tabstop=8: