Storage Administration GuideChapter 8. The XFS File SystemXFS is a highly scalable, high-performance file system which was originally designed at Silicon Graphics, Inc. It was created to support extremely large filesystems (up to 16 exabytes), files (8 exabytes) and directory structures (tens of millions of entries). - Main Features
XFS supports metadata journaling, which facilitates quicker crash recovery. The XFS file system can also be defragmented and enlarged while mounted and active. In addition, Red Hat Enterprise Linux 6 supports backup and restore utilities specific to XFS. - Allocation Features
XFS features the following allocation schemes: Delayed allocation and other performance optimizations affect XFS the same way that they do ext4. Namely, a program's writes to an XFS file system are not guaranteed to be on-disk unless the program issues an fsync() call afterwards. For more information on the implications of delayed allocation on a file system, refer to Allocation Features in Chapter 6, The Ext4 File System. The workaround for ensuring writes to disk applies to XFS as well. - Other XFS Features
The XFS file system also supports the following: Extended attributes (xattr), which allows the system to associate several additional name/value pairs per file. Quota journaling, which avoids the need for lengthy quota consistency checks after a crash. Project/directory quotas, allowing quota restrictions over a directory tree. Subsecond timestamps
8.1. Creating an XFS File SystemTo create an XFS file system, use the mkfs.xfs /dev/device command. In general, the default options are optimal for common use. When using mkfs.xfs on a block device containing an existing file system, use the -f option to force an overwrite of that file system. Example 8.1. Output of the mkfs.xfs command Below is a sample output of the mkfs.xfs command: meta-data=/dev/device isize=256 agcount=4, agsize=3277258 blks = sectsz=512 attr=2data = bsize=4096 blocks=13109032, imaxpct=25 = sunit=0 swidth=0 blksnaming =version 2 bsize=4096 ascii-ci=0log =internal log bsize=4096 blocks=6400, version=2 = sectsz=512 sunit=0 blks, lazy-count=1realtime =none extsz=4096 blocks=0, rtextents=0 For striped block devices (e.g., RAID5 arrays), the stripe geometry can be specified at the time of file system creation. Using proper stripe geometry greatly enhances the performance of an XFS filesystem. When creating filesystems on lvm or md volumes, mkfs.xfs chooses an optimal geometry. This may also be true on some hardware RAIDs which export geometry information to the operating system. To specify stripe geometry, use the following mkfs.xfs sub-options: - su=
value Specifies a stripe unit or RAID chunk size. The valuek, m, or g suffix. - sw=
value Specifies the number of data disks in a RAID device, or the number of stripe units in the stripe.
The following example specifies a chunk size of 64k on a RAID device containing 4 stripe units: mkfs.xfs -d su=64k,sw=4 /dev/device
For more information about creating XFS file systems, refer to man mkfs.xfs. 8.2. Mounting an XFS File SystemAn XFS file system can be mounted with no extra options, for example: mount /dev/device /mount/point
XFS also supports several mount options to influence behavior. By default, XFS allocates inodes to reflect their on-disk location. However, because some 32-bit userspace applications are not compatible with inode numbers greater than 232, XFS will allocate all inodes in disk locations which result in 32-bit inode numbers. This can lead to decreased performance on very large filesystems (i.e. larger than 2 terabytes), because inodes are skewed to the beginning of the block device, while data is skewed towards the end. To address this, use the inode64 mount option. This option configures XFS to allocate inodes and data across the entire file system, which can improve performance: # mount -o inode64 /dev/device /mount/point By default, XFS uses write barriers to ensure file system integrity even when power is lost to a device with write caches enabled. For devices without write caches, or with battery-backed write caches, disable barriers using the nobarrier option: # mount -o nobarrier /dev/device /mount/point 8.3. XFS Quota ManagementThe XFS quota subsystem manages limits on disk space (blocks) and file (inode) usage. XFS quotas control and/or report on usage of these items on a user, group, or directory/project level. Also, note that while user, group, and directory/project quotas are enabled independently, group and project quotas are mutually exclusive. When managing on a per-directory or per-project basis, XFS manages the disk usage of directory hierarchies associated with a specific project. In doing so, XFS recognizes cross-organizational "group" boundaries between projects. This provides a level of control that is broader than what is available when managing quotas for users or groups. XFS quotas are enabled at mount time, with specific mount options. Each mount option can also be specified as noenforce; this will allow usage reporting without enforcing any limits. Valid quota mount options are: uquota/uqnoenforce - User quotas
gquota/gqnoenforce - Group quotas
pquota/pqnoenforce - Project quota
Once quotas are enabled, the xfs_quota tool can be used to set limits and report on disk usage. By default, xfs_quota is run interactively, and in basic mode. Basic mode sub-commands simply report usage, and are available to all users. Basic xfs_quota sub-commands include: - quota
username/userID Show usage and limits for the given usernameuserID - df
Shows free and used counts for blocks and inodes.
In contrast, xfs_quota also has an expert mode. The sub-commands of this mode allow actual configuration of limits, and are available only to users with elevated privileges. To use expert mode sub-commands interactively, run xfs_quota -x. Expert mode sub-commands include: - report
/path Reports quota information for a specific file system. - limit
Modify quota limits.
For a complete list of sub-commands for either basic or expert mode, use the sub-command help. All sub-commands can also be run directly from a command line using the -c option, with -x for expert sub-commands. Example 8.2. Display a sample quota report For example, to display a sample quota report for /home (on /dev/blockdevice), use the command xfs_quota -cx 'report -h' /home. This will display output similar to the following: User quota on /home (/dev/blockdevice) Blocks User ID Used Soft Hard Warn/Grace ---------- --------------------------------- root 0 0 0 00 [------]testuser 103.4G 0 0 00 [------]... To set a soft and hard inode count limit of 500 and 700 respectively for user john (whose home directory is /home/john), use the following command: # xfs_quota -x -c 'limit isoft=500 ihard=700 /home/john' By default, the limit sub-command recognizes targets as users. When configuring the limits for a group, use the -g option (as in the previous example). Similarly, use -p for projects. Soft and hard block limits can also be configured using bsoft/bhard instead of isoft/ihard. Example 8.3. Set a soft and hard block limit For example, to set a soft and hard block limit of 1000m and 1200m, respectively, to group accounting on the /target/path file system, use the following command: # xfs_quota -x -c 'limit -g bsoft=1000m bhard=1200m accounting' /target/path While real-time blocks (rtbhard/rtbsoft) are described in man xfs_quota as valid units when setting quotas, the real-time sub-volume is not enabled in this release. As such, the rtbhard and rtbsoft options are not applicable. Before configuring limits for project-controlled directories, add them first to /etc/projects. Project names can be added to/etc/projectid to map project IDs to project names. Once a project is added to /etc/projects, initialize its project directory using the following command: # xfs_quota -c 'project -s projectname' Quotas for projects with initialized directories can then be configured, as in: # xfs_quota -x -c 'limit -p bsoft=1000m bhard=1200m projectname' Generic quota configuration tools (e.g. quota, repquota, edquota) may also be used to manipulate XFS quotas. However, these tools cannot be used with XFS project quotas. For more information about setting XFS quotas, refer to man xfs_quota. 8.4. Increasing the Size of an XFS File SystemAn XFS file system may be grown while mounted using the xfs_growfs command: # xfs_growfs /mount/point -D size The -D size option grows the file system to the specified size-D size option, xfs_growfs will grow the file system to the maximum size supported by the device. Before growing an XFS file system with -D size, ensure that the underlying block device is of an appropriate size to hold the file system later. Use the appropriate resizing methods for the affected block device. While XFS file systems can be grown while mounted, their size cannot be reduced at all. For more information about growing a file system, refer to man xfs_growfs. 8.5. Repairing an XFS File SystemTo repair an XFS file system, use xfs_repair: # xfs_repair /dev/device The xfs_repair utility is highly scalable, and is designed to repair even very large file systems with many inodes efficiently. Note that unlike other Linux file systems, xfs_repair does not run at boot time, even when an XFS file system was not cleanly unmounted. In the event of an unclean unmount, xfs_repair simply replays the log at mount time, ensuring a consistent file system. The xfs_repair utility cannot repair an XFS file system with a dirty log. To clear the log, mount and unmount the XFS file system. If the log is corrupt and cannot be replayed, use the -L option ("force log zeroing") to clear the log, i.e. xfs_repair -L /dev/device. Note, however, that this may result in further corruption or data loss. For more information about repairing an XFS file system, refer to man xfs_repair. 8.6. Suspending an XFS File SystemTo suspend or resume write activity to a file system, use xfs_freeze. Suspending write activity allows hardware-based device snapshots to be used to capture the file system in a consistent state. The xfs_freeze utility is provided by the xfsprogs package, which is only available on x86_64. To suspend (i.e. freeze) an XFS file system, use: # xfs_freeze -f /mount/point To unfreeze an XFS file system, use: # xfs_freeze -u /mount/point When taking an LVM snapshot, it is not necessary to use xfs_freeze to suspend the file system first. Rather, the LVM management tools will automatically suspend the XFS file system before taking the snapshot. You can also use the xfs_freeze utility to freeze/unfreeze an ext3, ext4, GFS2, XFS, and BTRFS, file system. The syntax for doing so is also the same. For more information about freezing and unfreezing an XFS file system, refer to man xfs_freeze. 8.7. Backup and Restoration of XFS File SystemsXFS file system backup and restoration involves two utilities: xfsdump and xfsrestore. To backup or dump an XFS file system, use the xfsdump utility. Red Hat Enterprise Linux 6 supports backups to tape drives or regular file images, and also allows multiple dumps to be written to the same tape. The xfsdump utility also allows a dump to span multiple tapes, although only one dump can be written to a regular file. In addition, xfsdump supports incremental backups, and can exclude files from a backup using size, subtree, or inode flags to filter them. In order to support incremental backups, xfsdump uses dump levels to determine a base dump to which a specific dump is relative. The -l option specifies a dump level (0-9). To perform a full backup, perform a level 0 dump on the file system (i.e. /path/to/filesystem # xfsdump -l 0 -f /dev/device /path/to/filesystem The -f option specifies a destination for a backup. For example, the /dev/st0 destination is normally used for tape drives. An xfsdump destination can be a tape drive, regular file, or remote tape device. In contrast, an incremental backup will only dump files that changed since the last level 0 dump. A level 1 dump is the first incremental dump after a full dump; the next incremental dump would be level 2, and so on, to a maximum of level 9. So, to perform a level 1 dump to a tape drive: # xfsdump -l 1 -f /dev/st0 /path/to/filesystem Conversely, the xfsrestore utility restores file systems from dumps produced by xfsdump. The xfsrestore utility has two modes: a default simple mode, and a cumulative mode. Specific dumps are identified by session ID or session label. As such, restoring a dump requires its corresponding session ID or label. To display the session ID and labels of all dumps (both full and incremental), use the -I option: # xfsrestore -I This will provide output similar to the following: Example 8.4. Session ID and labels of all dumps file system 0:fs id:45e9af35-efd2-4244-87bc-4762e476cbabsession 0:mount point:bear-05:/mnt/testdevice:bear-05:/dev/sdb2time:Fri Feb 26 16:55:21 2010session label:"my_dump_session_label"session id:b74a3586-e52e-4a4a-8775-c3334fa8ea2clevel:0resumed:NOsubtree:NOstreams:1stream 0:pathname:/mnt/test2/backupstart:ino 0 offset 0end:ino 1 offset 0interrupted:NOmedia files:1media file 0:mfile index:0mfile type:datamfile size:21016mfile start:ino 0 offset 0mfile end:ino 1 offset 0media label:"my_dump_media_label"media id:4a518062-2a8f-4f17-81fd-bb1eb2e3cb4fxfsrestore: Restore Status: SUCCESS The simple mode allows users to restore an entire file system from a level 0 dump. After identifying a level 0 dump's session ID (i.e. session-ID/path/to/destination # xfsrestore -f /dev/st0 -S session-ID /path/to/destination The -f option specifies the location of the dump, while the -S or -L option specifies which specific dump to restore. The -S option is used to specify a session ID, while the -L option is used for session labels. The -I option displays both session labels and IDs for each dump. xfsrestore Cumulative ModeThe cumulative mode of xfsrestore allows file system restoration from a specific incremental backup, i.e. level 1 to level 9. To restore a file system from an incremental backup, simply add the -r option: # xfsrestore -f /dev/st0 -S session-ID -r /path/to/destination The xfsrestore utility also allows specific files from a dump to be extracted, added, or deleted. To use xfsrestore interactively, use the -i option, as in: xfsrestore -f /dev/st0 -i
The interactive dialogue will begin after xfsrestore finishes reading the specified device. Available commands in this dialogue include cd, ls, add, delete, and extract; for a complete list of commands, use help. For more information about dumping and restoring XFS file systems, refer to man xfsdump and man xfsrestore. 8.8. Other XFS File System UtilitiesRed Hat Enterprise Linux 6 also features other utilities for managing XFS file systems: - xfs_fsr
Used to defragment mounted XFS file systems. When invoked with no arguments, xfs_fsr defragments all regular files in all mounted XFS file systems. This utility also allows users to suspend a defragmentation at a specified time and resume from where it left off later. In addition, xfs_fsr also allows the defragmentation of only one file, as in xfs_fsr /path/to/file. Red Hat advises against periodically defragmenting an entire file system, as this is normally not warranted. - xfs_bmap
Prints the map of disk blocks used by files in an XFS filesystem. This map lists each extent used by a specified file, as well as regions in the file with no corresponding blocks (i.e. holes). - xfs_info
Prints XFS file system information. - xfs_admin
Changes the parameters of an XFS file system. The xfs_admin utility can only modify parameters of unmounted devices/file systems. - xfs_copy
Copies the contents of an entire XFS file system to one or more targets in parallel.
The following utilities are also useful in debugging and analyzing XFS file systems: - xfs_metadump
Copies XFS file system metadata to a file. The xfs_metadump utility should only be used to copy unmounted, read-only, or frozen/suspended file systems; otherwise, generated dumps could be corrupted or inconsistent. - xfs_mdrestore
Restores and XFS metadump image (generated using xfs_metadump) to a file system image. - xfs_db
Debugs an XFS file system.
For more information about these utilities, refer to their respective man pages. |
