The SGI XFS Filesystem ====================== XFS is a high performance journaling filesystem which originated on the SGI IRIX platform. It is completely multi-threaded, can support large files and large filesystems, extended attributes, variable block sizes, is extent based, and makes extensive use of Btrees (directories, extents, free space) to aid both performance and scalability. Refer to the documentation at http://oss.sgi.com/projects/xfs/ for further details. This implementation is on-disk compatible with the IRIX version of XFS. Mount Options ============= When mounting an XFS filesystem, the following options are accepted. For boolean mount options, the names with the (*) suffix is the default behaviour. allocsize=size Sets the buffered I/O end-of-file preallocation size when doing delayed allocation writeout (default size is 64KiB). Valid values for this option are page size (typically 4KiB) through to 1GiB, inclusive, in power-of-2 increments. The default behaviour is for dynamic end-of-file preallocation size, which uses a set of heuristics to optimise the preallocation size based on the current allocation patterns within the file and the access patterns to the file. Specifying a fixed allocsize value turns off the dynamic behaviour. attr2 noattr2 The options enable/disable an "opportunistic" improvement to be made in the way inline extended attributes are stored on-disk. When the new form is used for the first time when attr2 is selected (either when setting or removing extended attributes) the on-disk superblock feature bit field will be updated to reflect this format being in use. The default behaviour is determined by the on-disk feature bit indicating that attr2 behaviour is active. If either mount option it set, then that becomes the new default used by the filesystem. CRC enabled filesystems always use the attr2 format, and so will reject the noattr2 mount option if it is set. barrier (*) nobarrier Enables/disables the use of block layer write barriers for writes into the journal and for data integrity operations. This allows for drive level write caching to be enabled, for devices that support write barriers. discard nodiscard (*) Enable/disable the issuing of commands to let the block device reclaim space freed by the filesystem. This is useful for SSD devices, thinly provisioned LUNs and virtual machine images, but may have a performance impact. Note: It is currently recommended that you use the fstrim application to discard unused blocks rather than the discard mount option because the performance impact of this option is quite severe. grpid/bsdgroups nogrpid/sysvgroups (*) These options define what group ID a newly created file gets. When grpid is set, it takes the group ID of the directory in which it is created; otherwise it takes the fsgid of the current process, unless the directory has the setgid bit set, in which case it takes the gid from the parent directory, and also gets the setgid bit set if it is a directory itself. filestreams Make the data allocator use the filestreams allocation mode across the entire filesystem rather than just on directories configured to use it. ikeep noikeep (*) When ikeep is specified, XFS does not delete empty inode clusters and keeps them around on disk. When noikeep is specified, empty inode clusters are returned to the free space pool. inode32 inode64 (*) When inode32 is specified, it indicates that XFS limits inode creation to locations which will not result in inode numbers with more than 32 bits of significance. When inode64 is specified, it indicates that XFS is allowed to create inodes at any location in the filesystem, including those which will result in inode numbers occupying more than 32 bits of significance. inode32 is provided for backwards compatibility with older systems and applications, since 64 bits inode numbers might cause problems for some applications that cannot handle large inode numbers. If applications are in use which do not handle inode numbers bigger than 32 bits, the inode32 option should be specified. largeio nolargeio (*) If "nolargeio" is specified, the optimal I/O reported in st_blksize by stat(2) will be as small as possible to allow user applications to avoid inefficient read/modify/write I/O. This is typically the page size of the machine, as this is the granularity of the page cache. If "largeio" specified, a filesystem that was created with a "swidth" specified will return the "swidth" value (in bytes) in st_blksize. If the filesystem does not have a "swidth" specified but does specify an "allocsize" then "allocsize" (in bytes) will be returned instead. Otherwise the behaviour is the same as if "nolargeio" was specified. logbufs=value Set the number of in-memory log buffers. Valid numbers range from 2-8 inclusive. The default value is 8 buffers. If the memory cost of 8 log buffers is too high on small systems, then it may be reduced at some cost to performance on metadata intensive workloads. The logbsize option below controls the size of each buffer and so is also relevent to this case. logbsize=value Set the size of each in-memory log buffer. The size may be specified in bytes, or in kilobytes with a "k" suffix. Valid sizes for version 1 and version 2 logs are 16384 (16k) and 32768 (32k). Valid sizes for version 2 logs also include 65536 (64k), 131072 (128k) and 262144 (256k). The logbsize must be an integer multiple of the log stripe unit configured at mkfs time. The default value for for version 1 logs is 32768, while the default value for version 2 logs is MAX(32768, log_sunit). logdev=device and rtdev=device Use an external log (metadata journal) and/or real-time device. An XFS filesystem has up to three parts: a data section, a log section, and a real-time section. The real-time section is optional, and the log section can be separate from the data section or contained within it. noalign Data allocations will not be aligned at stripe unit boundaries. This is only relevant to filesystems created with non-zero data alignment parameters (sunit, swidth) by mkfs. norecovery The filesystem will be mounted without running log recovery. If the filesystem was not cleanly unmounted, it is likely to be inconsistent when mounted in "norecovery" mode. Some files or directories may not be accessible because of this. Filesystems mounted "norecovery" must be mounted read-only or the mount will fail. nouuid Don't check for double mounted file systems using the file system uuid. This is useful to mount LVM snapshot volumes, and often used in combination with "norecovery" for mounting read-only snapshots. noquota Forcibly turns off all quota accounting and enforcement within the filesystem. uquota/usrquota/uqnoenforce/quota User disk quota accounting enabled, and limits (optionally) enforced. Refer to xfs_quota(8) for further details. gquota/grpquota/gqnoenforce Group disk quota accounting enabled and limits (optionally) enforced. Refer to xfs_quota(8) for further details. pquota/prjquota/pqnoenforce Project disk quota accounting enabled and limits (optionally) enforced. Refer to xfs_quota(8) for further details. sunit=value and swidth=value Used to specify the stripe unit and width for a RAID device or a stripe volume. "value" must be specified in 512-byte block units. These options are only relevant to filesystems that were created with non-zero data alignment parameters. The sunit and swidth parameters specified must be compatible with the existing filesystem alignment characteristics. In general, that means the only valid changes to sunit are increasing it by a power-of-2 multiple. Valid swidth values are any integer multiple of a valid sunit value. Typically the only time these mount options are necessary if after an underlying RAID device has had it's geometry modified, such as adding a new disk to a RAID5 lun and reshaping it. swalloc Data allocations will be rounded up to stripe width boundaries when the current end of file is being extended and the file size is larger than the stripe width size. wsync When specified, all filesystem namespace operations are executed synchronously. This ensures that when the namespace operation (create, unlink, etc) completes, the change to the namespace is on stable storage. This is useful in HA setups where failover must not result in clients seeing inconsistent namespace presentation during or after a failover event. Deprecated Mount Options ======================== delaylog/nodelaylog Delayed logging is the only logging method that XFS supports now, so these mount options are now ignored. Due for removal in 3.12. ihashsize=value In memory inode hashes have been removed, so this option has no function as of August 2007. Option is deprecated. Due for removal in 3.12. irixsgid This behaviour is now controlled by a sysctl, so the mount option is ignored. Due for removal in 3.12. osyncisdsync osyncisosync O_SYNC and O_DSYNC are fully supported, so there is no need for these options any more. Due for removal in 3.12. sysctls ======= The following sysctls are available for the XFS filesystem: fs.xfs.stats_clear (Min: 0 Default: 0 Max: 1) Setting this to "1" clears accumulated XFS statistics in /proc/fs/xfs/stat. It then immediately resets to "0". fs.xfs.xfssyncd_centisecs (Min: 100 Default: 3000 Max: 720000) The interval at which the filesystem flushes metadata out to disk and runs internal cache cleanup routines. fs.xfs.filestream_centisecs (Min: 1 Default: 3000 Max: 360000) The interval at which the filesystem ages filestreams cache references and returns timed-out AGs back to the free stream pool. fs.xfs.speculative_prealloc_lifetime (Units: seconds Min: 1 Default: 300 Max: 86400) The interval at which the background scanning for inodes with unused speculative preallocation runs. The scan removes unused preallocation from clean inodes and releases the unused space back to the free pool. fs.xfs.error_level (Min: 0 Default: 3 Max: 11) A volume knob for error reporting when internal errors occur. This will generate detailed messages & backtraces for filesystem shutdowns, for example. Current threshold values are: XFS_ERRLEVEL_OFF: 0 XFS_ERRLEVEL_LOW: 1 XFS_ERRLEVEL_HIGH: 5 fs.xfs.panic_mask (Min: 0 Default: 0 Max: 127) Causes certain error conditions to call BUG(). Value is a bitmask; AND together the tags which represent errors which should cause panics: XFS_NO_PTAG 0 XFS_PTAG_IFLUSH 0x00000001 XFS_PTAG_LOGRES 0x00000002 XFS_PTAG_AILDELETE 0x00000004 XFS_PTAG_ERROR_REPORT 0x00000008 XFS_PTAG_SHUTDOWN_CORRUPT 0x00000010 XFS_PTAG_SHUTDOWN_IOERROR 0x00000020 XFS_PTAG_SHUTDOWN_LOGERROR 0x00000040 This option is intended for debugging only. fs.xfs.irix_symlink_mode (Min: 0 Default: 0 Max: 1) Controls whether symlinks are created with mode 0777 (default) or whether their mode is affected by the umask (irix mode). fs.xfs.irix_sgid_inherit (Min: 0 Default: 0 Max: 1) Controls files created in SGID directories. If the group ID of the new file does not match the effective group ID or one of the supplementary group IDs of the parent dir, the ISGID bit is cleared if the irix_sgid_inherit compatibility sysctl is set. fs.xfs.inherit_sync (Min: 0 Default: 1 Max: 1) Setting this to "1" will cause the "sync" flag set by the xfs_io(8) chattr command on a directory to be inherited by files in that directory. fs.xfs.inherit_nodump (Min: 0 Default: 1 Max: 1) Setting this to "1" will cause the "nodump" flag set by the xfs_io(8) chattr command on a directory to be inherited by files in that directory. fs.xfs.inherit_noatime (Min: 0 Default: 1 Max: 1) Setting this to "1" will cause the "noatime" flag set by the xfs_io(8) chattr command on a directory to be inherited by files in that directory. fs.xfs.inherit_nosymlinks (Min: 0 Default: 1 Max: 1) Setting this to "1" will cause the "nosymlinks" flag set by the xfs_io(8) chattr command on a directory to be inherited by files in that directory. fs.xfs.inherit_nodefrag (Min: 0 Default: 1 Max: 1) Setting this to "1" will cause the "nodefrag" flag set by the xfs_io(8) chattr command on a directory to be inherited by files in that directory. fs.xfs.rotorstep (Min: 1 Default: 1 Max: 256) In "inode32" allocation mode, this option determines how many files the allocator attempts to allocate in the same allocation group before moving to the next allocation group. The intent is to control the rate at which the allocator moves between allocation groups when allocating extents for new files. Deprecated Sysctls ================== fs.xfs.xfsbufd_centisecs (Min: 50 Default: 100 Max: 3000) Dirty metadata is now tracked by the log subsystem and flushing is driven by log space and idling demands. The xfsbufd no longer exists, so this syctl does nothing. Due for removal in 3.14. fs.xfs.age_buffer_centisecs (Min: 100 Default: 1500 Max: 720000) Dirty metadata is now tracked by the log subsystem and flushing is driven by log space and idling demands. The xfsbufd no longer exists, so this syctl does nothing. Due for removal in 3.14.