linux/Documentation/filesystems/xfs.txt
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   1
   2The SGI XFS Filesystem
   3======================
   4
   5XFS is a high performance journaling filesystem which originated
   6on the SGI IRIX platform.  It is completely multi-threaded, can
   7support large files and large filesystems, extended attributes,
   8variable block sizes, is extent based, and makes extensive use of
   9Btrees (directories, extents, free space) to aid both performance
  10and scalability.
  11
  12Refer to the documentation at http://oss.sgi.com/projects/xfs/
  13for further details.  This implementation is on-disk compatible
  14with the IRIX version of XFS.
  15
  16
  17Mount Options
  18=============
  19
  20When mounting an XFS filesystem, the following options are accepted.
  21For boolean mount options, the names with the (*) suffix is the
  22default behaviour.
  23
  24  allocsize=size
  25        Sets the buffered I/O end-of-file preallocation size when
  26        doing delayed allocation writeout (default size is 64KiB).
  27        Valid values for this option are page size (typically 4KiB)
  28        through to 1GiB, inclusive, in power-of-2 increments.
  29
  30        The default behaviour is for dynamic end-of-file
  31        preallocation size, which uses a set of heuristics to
  32        optimise the preallocation size based on the current
  33        allocation patterns within the file and the access patterns
  34        to the file. Specifying a fixed allocsize value turns off
  35        the dynamic behaviour.
  36
  37  attr2
  38  noattr2
  39        The options enable/disable an "opportunistic" improvement to
  40        be made in the way inline extended attributes are stored
  41        on-disk.  When the new form is used for the first time when
  42        attr2 is selected (either when setting or removing extended
  43        attributes) the on-disk superblock feature bit field will be
  44        updated to reflect this format being in use.
  45
  46        The default behaviour is determined by the on-disk feature
  47        bit indicating that attr2 behaviour is active. If either
  48        mount option it set, then that becomes the new default used
  49        by the filesystem.
  50
  51        CRC enabled filesystems always use the attr2 format, and so
  52        will reject the noattr2 mount option if it is set.
  53
  54  barrier (*)
  55  nobarrier
  56        Enables/disables the use of block layer write barriers for
  57        writes into the journal and for data integrity operations.
  58        This allows for drive level write caching to be enabled, for
  59        devices that support write barriers.
  60
  61  discard
  62  nodiscard (*)
  63        Enable/disable the issuing of commands to let the block
  64        device reclaim space freed by the filesystem.  This is
  65        useful for SSD devices, thinly provisioned LUNs and virtual
  66        machine images, but may have a performance impact.
  67
  68        Note: It is currently recommended that you use the fstrim
  69        application to discard unused blocks rather than the discard
  70        mount option because the performance impact of this option
  71        is quite severe.
  72
  73  grpid/bsdgroups
  74  nogrpid/sysvgroups (*)
  75        These options define what group ID a newly created file
  76        gets.  When grpid is set, it takes the group ID of the
  77        directory in which it is created; otherwise it takes the
  78        fsgid of the current process, unless the directory has the
  79        setgid bit set, in which case it takes the gid from the
  80        parent directory, and also gets the setgid bit set if it is
  81        a directory itself.
  82
  83  filestreams
  84        Make the data allocator use the filestreams allocation mode
  85        across the entire filesystem rather than just on directories
  86        configured to use it.
  87
  88  ikeep
  89  noikeep (*)
  90        When ikeep is specified, XFS does not delete empty inode
  91        clusters and keeps them around on disk.  When noikeep is
  92        specified, empty inode clusters are returned to the free
  93        space pool.
  94
  95  inode32
  96  inode64 (*)
  97        When inode32 is specified, it indicates that XFS limits
  98        inode creation to locations which will not result in inode
  99        numbers with more than 32 bits of significance.
 100
 101        When inode64 is specified, it indicates that XFS is allowed
 102        to create inodes at any location in the filesystem,
 103        including those which will result in inode numbers occupying
 104        more than 32 bits of significance. 
 105
 106        inode32 is provided for backwards compatibility with older
 107        systems and applications, since 64 bits inode numbers might
 108        cause problems for some applications that cannot handle
 109        large inode numbers.  If applications are in use which do
 110        not handle inode numbers bigger than 32 bits, the inode32
 111        option should be specified.
 112
 113
 114  largeio
 115  nolargeio (*)
 116        If "nolargeio" is specified, the optimal I/O reported in
 117        st_blksize by stat(2) will be as small as possible to allow
 118        user applications to avoid inefficient read/modify/write
 119        I/O.  This is typically the page size of the machine, as
 120        this is the granularity of the page cache.
 121
 122        If "largeio" specified, a filesystem that was created with a
 123        "swidth" specified will return the "swidth" value (in bytes)
 124        in st_blksize. If the filesystem does not have a "swidth"
 125        specified but does specify an "allocsize" then "allocsize"
 126        (in bytes) will be returned instead. Otherwise the behaviour
 127        is the same as if "nolargeio" was specified.
 128
 129  logbufs=value
 130        Set the number of in-memory log buffers.  Valid numbers
 131        range from 2-8 inclusive.
 132
 133        The default value is 8 buffers.
 134
 135        If the memory cost of 8 log buffers is too high on small
 136        systems, then it may be reduced at some cost to performance
 137        on metadata intensive workloads. The logbsize option below
 138        controls the size of each buffer and so is also relevent to
 139        this case.
 140
 141  logbsize=value
 142        Set the size of each in-memory log buffer.  The size may be
 143        specified in bytes, or in kilobytes with a "k" suffix.
 144        Valid sizes for version 1 and version 2 logs are 16384 (16k)
 145        and 32768 (32k).  Valid sizes for version 2 logs also
 146        include 65536 (64k), 131072 (128k) and 262144 (256k). The
 147        logbsize must be an integer multiple of the log
 148        stripe unit configured at mkfs time.
 149
 150        The default value for for version 1 logs is 32768, while the
 151        default value for version 2 logs is MAX(32768, log_sunit).
 152
 153  logdev=device and rtdev=device
 154        Use an external log (metadata journal) and/or real-time device.
 155        An XFS filesystem has up to three parts: a data section, a log
 156        section, and a real-time section.  The real-time section is
 157        optional, and the log section can be separate from the data
 158        section or contained within it.
 159
 160  noalign
 161        Data allocations will not be aligned at stripe unit
 162        boundaries. This is only relevant to filesystems created
 163        with non-zero data alignment parameters (sunit, swidth) by
 164        mkfs.
 165
 166  norecovery
 167        The filesystem will be mounted without running log recovery.
 168        If the filesystem was not cleanly unmounted, it is likely to
 169        be inconsistent when mounted in "norecovery" mode.
 170        Some files or directories may not be accessible because of this.
 171        Filesystems mounted "norecovery" must be mounted read-only or
 172        the mount will fail.
 173
 174  nouuid
 175        Don't check for double mounted file systems using the file
 176        system uuid.  This is useful to mount LVM snapshot volumes,
 177        and often used in combination with "norecovery" for mounting
 178        read-only snapshots.
 179
 180  noquota
 181        Forcibly turns off all quota accounting and enforcement
 182        within the filesystem.
 183
 184  uquota/usrquota/uqnoenforce/quota
 185        User disk quota accounting enabled, and limits (optionally)
 186        enforced.  Refer to xfs_quota(8) for further details.
 187
 188  gquota/grpquota/gqnoenforce
 189        Group disk quota accounting enabled and limits (optionally)
 190        enforced.  Refer to xfs_quota(8) for further details.
 191
 192  pquota/prjquota/pqnoenforce
 193        Project disk quota accounting enabled and limits (optionally)
 194        enforced.  Refer to xfs_quota(8) for further details.
 195
 196  sunit=value and swidth=value
 197        Used to specify the stripe unit and width for a RAID device
 198        or a stripe volume.  "value" must be specified in 512-byte
 199        block units. These options are only relevant to filesystems
 200        that were created with non-zero data alignment parameters.
 201
 202        The sunit and swidth parameters specified must be compatible
 203        with the existing filesystem alignment characteristics.  In
 204        general, that means the only valid changes to sunit are
 205        increasing it by a power-of-2 multiple. Valid swidth values
 206        are any integer multiple of a valid sunit value.
 207
 208        Typically the only time these mount options are necessary if
 209        after an underlying RAID device has had it's geometry
 210        modified, such as adding a new disk to a RAID5 lun and
 211        reshaping it.
 212
 213  swalloc
 214        Data allocations will be rounded up to stripe width boundaries
 215        when the current end of file is being extended and the file
 216        size is larger than the stripe width size.
 217
 218  wsync
 219        When specified, all filesystem namespace operations are
 220        executed synchronously. This ensures that when the namespace
 221        operation (create, unlink, etc) completes, the change to the
 222        namespace is on stable storage. This is useful in HA setups
 223        where failover must not result in clients seeing
 224        inconsistent namespace presentation during or after a
 225        failover event.
 226
 227
 228Deprecated Mount Options
 229========================
 230
 231  delaylog/nodelaylog
 232        Delayed logging is the only logging method that XFS supports
 233        now, so these mount options are now ignored.
 234
 235        Due for removal in 3.12.
 236
 237  ihashsize=value
 238        In memory inode hashes have been removed, so this option has
 239        no function as of August 2007. Option is deprecated.
 240
 241        Due for removal in 3.12.
 242
 243  irixsgid
 244        This behaviour is now controlled by a sysctl, so the mount
 245        option is ignored.
 246
 247        Due for removal in 3.12.
 248
 249  osyncisdsync
 250  osyncisosync
 251        O_SYNC and O_DSYNC are fully supported, so there is no need
 252        for these options any more.
 253
 254        Due for removal in 3.12.
 255
 256sysctls
 257=======
 258
 259The following sysctls are available for the XFS filesystem:
 260
 261  fs.xfs.stats_clear            (Min: 0  Default: 0  Max: 1)
 262        Setting this to "1" clears accumulated XFS statistics
 263        in /proc/fs/xfs/stat.  It then immediately resets to "0".
 264
 265  fs.xfs.xfssyncd_centisecs     (Min: 100  Default: 3000  Max: 720000)
 266        The interval at which the filesystem flushes metadata
 267        out to disk and runs internal cache cleanup routines.
 268
 269  fs.xfs.filestream_centisecs   (Min: 1  Default: 3000  Max: 360000)
 270        The interval at which the filesystem ages filestreams cache
 271        references and returns timed-out AGs back to the free stream
 272        pool.
 273
 274  fs.xfs.speculative_prealloc_lifetime
 275                (Units: seconds   Min: 1  Default: 300  Max: 86400)
 276        The interval at which the background scanning for inodes
 277        with unused speculative preallocation runs. The scan
 278        removes unused preallocation from clean inodes and releases
 279        the unused space back to the free pool.
 280
 281  fs.xfs.error_level            (Min: 0  Default: 3  Max: 11)
 282        A volume knob for error reporting when internal errors occur.
 283        This will generate detailed messages & backtraces for filesystem
 284        shutdowns, for example.  Current threshold values are:
 285
 286                XFS_ERRLEVEL_OFF:       0
 287                XFS_ERRLEVEL_LOW:       1
 288                XFS_ERRLEVEL_HIGH:      5
 289
 290  fs.xfs.panic_mask             (Min: 0  Default: 0  Max: 127)
 291        Causes certain error conditions to call BUG(). Value is a bitmask;
 292        AND together the tags which represent errors which should cause panics:
 293
 294                XFS_NO_PTAG                     0
 295                XFS_PTAG_IFLUSH                 0x00000001
 296                XFS_PTAG_LOGRES                 0x00000002
 297                XFS_PTAG_AILDELETE              0x00000004
 298                XFS_PTAG_ERROR_REPORT           0x00000008
 299                XFS_PTAG_SHUTDOWN_CORRUPT       0x00000010
 300                XFS_PTAG_SHUTDOWN_IOERROR       0x00000020
 301                XFS_PTAG_SHUTDOWN_LOGERROR      0x00000040
 302
 303        This option is intended for debugging only.
 304
 305  fs.xfs.irix_symlink_mode      (Min: 0  Default: 0  Max: 1)
 306        Controls whether symlinks are created with mode 0777 (default)
 307        or whether their mode is affected by the umask (irix mode).
 308
 309  fs.xfs.irix_sgid_inherit      (Min: 0  Default: 0  Max: 1)
 310        Controls files created in SGID directories.
 311        If the group ID of the new file does not match the effective group
 312        ID or one of the supplementary group IDs of the parent dir, the
 313        ISGID bit is cleared if the irix_sgid_inherit compatibility sysctl
 314        is set.
 315
 316  fs.xfs.inherit_sync           (Min: 0  Default: 1  Max: 1)
 317        Setting this to "1" will cause the "sync" flag set
 318        by the xfs_io(8) chattr command on a directory to be
 319        inherited by files in that directory.
 320
 321  fs.xfs.inherit_nodump         (Min: 0  Default: 1  Max: 1)
 322        Setting this to "1" will cause the "nodump" flag set
 323        by the xfs_io(8) chattr command on a directory to be
 324        inherited by files in that directory.
 325
 326  fs.xfs.inherit_noatime        (Min: 0  Default: 1  Max: 1)
 327        Setting this to "1" will cause the "noatime" flag set
 328        by the xfs_io(8) chattr command on a directory to be
 329        inherited by files in that directory.
 330
 331  fs.xfs.inherit_nosymlinks     (Min: 0  Default: 1  Max: 1)
 332        Setting this to "1" will cause the "nosymlinks" flag set
 333        by the xfs_io(8) chattr command on a directory to be
 334        inherited by files in that directory.
 335
 336  fs.xfs.inherit_nodefrag       (Min: 0  Default: 1  Max: 1)
 337        Setting this to "1" will cause the "nodefrag" flag set
 338        by the xfs_io(8) chattr command on a directory to be
 339        inherited by files in that directory.
 340
 341  fs.xfs.rotorstep              (Min: 1  Default: 1  Max: 256)
 342        In "inode32" allocation mode, this option determines how many
 343        files the allocator attempts to allocate in the same allocation
 344        group before moving to the next allocation group.  The intent
 345        is to control the rate at which the allocator moves between
 346        allocation groups when allocating extents for new files.
 347
 348Deprecated Sysctls
 349==================
 350
 351  fs.xfs.xfsbufd_centisecs      (Min: 50  Default: 100  Max: 3000)
 352        Dirty metadata is now tracked by the log subsystem and
 353        flushing is driven by log space and idling demands. The
 354        xfsbufd no longer exists, so this syctl does nothing.
 355
 356        Due for removal in 3.14.
 357
 358  fs.xfs.age_buffer_centisecs   (Min: 100  Default: 1500  Max: 720000)
 359        Dirty metadata is now tracked by the log subsystem and
 360        flushing is driven by log space and idling demands. The
 361        xfsbufd no longer exists, so this syctl does nothing.
 362
 363        Due for removal in 3.14.
 364
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