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543 lines
21 KiB
.. SPDX-License-Identifier: GPL-2.0 |
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====================== |
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The SGI XFS Filesystem |
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====================== |
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XFS is a high performance journaling filesystem which originated |
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on the SGI IRIX platform. It is completely multi-threaded, can |
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support large files and large filesystems, extended attributes, |
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variable block sizes, is extent based, and makes extensive use of |
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Btrees (directories, extents, free space) to aid both performance |
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and scalability. |
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Refer to the documentation at https://xfs.wiki.kernel.org/ |
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for further details. This implementation is on-disk compatible |
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with the IRIX version of XFS. |
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Mount Options |
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============= |
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When mounting an XFS filesystem, the following options are accepted. |
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allocsize=size |
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Sets the buffered I/O end-of-file preallocation size when |
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doing delayed allocation writeout (default size is 64KiB). |
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Valid values for this option are page size (typically 4KiB) |
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through to 1GiB, inclusive, in power-of-2 increments. |
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The default behaviour is for dynamic end-of-file |
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preallocation size, which uses a set of heuristics to |
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optimise the preallocation size based on the current |
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allocation patterns within the file and the access patterns |
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to the file. Specifying a fixed ``allocsize`` value turns off |
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the dynamic behaviour. |
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attr2 or noattr2 |
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The options enable/disable an "opportunistic" improvement to |
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be made in the way inline extended attributes are stored |
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on-disk. When the new form is used for the first time when |
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``attr2`` is selected (either when setting or removing extended |
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attributes) the on-disk superblock feature bit field will be |
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updated to reflect this format being in use. |
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The default behaviour is determined by the on-disk feature |
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bit indicating that ``attr2`` behaviour is active. If either |
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mount option is set, then that becomes the new default used |
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by the filesystem. |
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CRC enabled filesystems always use the ``attr2`` format, and so |
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will reject the ``noattr2`` mount option if it is set. |
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discard or nodiscard (default) |
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Enable/disable the issuing of commands to let the block |
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device reclaim space freed by the filesystem. This is |
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useful for SSD devices, thinly provisioned LUNs and virtual |
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machine images, but may have a performance impact. |
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Note: It is currently recommended that you use the ``fstrim`` |
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application to ``discard`` unused blocks rather than the ``discard`` |
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mount option because the performance impact of this option |
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is quite severe. |
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grpid/bsdgroups or nogrpid/sysvgroups (default) |
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These options define what group ID a newly created file |
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gets. When ``grpid`` is set, it takes the group ID of the |
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directory in which it is created; otherwise it takes the |
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``fsgid`` of the current process, unless the directory has the |
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``setgid`` bit set, in which case it takes the ``gid`` from the |
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parent directory, and also gets the ``setgid`` bit set if it is |
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a directory itself. |
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filestreams |
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Make the data allocator use the filestreams allocation mode |
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across the entire filesystem rather than just on directories |
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configured to use it. |
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ikeep or noikeep (default) |
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When ``ikeep`` is specified, XFS does not delete empty inode |
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clusters and keeps them around on disk. When ``noikeep`` is |
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specified, empty inode clusters are returned to the free |
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space pool. |
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inode32 or inode64 (default) |
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When ``inode32`` is specified, it indicates that XFS limits |
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inode creation to locations which will not result in inode |
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numbers with more than 32 bits of significance. |
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When ``inode64`` is specified, it indicates that XFS is allowed |
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to create inodes at any location in the filesystem, |
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including those which will result in inode numbers occupying |
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more than 32 bits of significance. |
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``inode32`` is provided for backwards compatibility with older |
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systems and applications, since 64 bits inode numbers might |
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cause problems for some applications that cannot handle |
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large inode numbers. If applications are in use which do |
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not handle inode numbers bigger than 32 bits, the ``inode32`` |
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option should be specified. |
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largeio or nolargeio (default) |
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If ``nolargeio`` is specified, the optimal I/O reported in |
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``st_blksize`` by **stat(2)** will be as small as possible to allow |
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user applications to avoid inefficient read/modify/write |
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I/O. This is typically the page size of the machine, as |
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this is the granularity of the page cache. |
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If ``largeio`` is specified, a filesystem that was created with a |
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``swidth`` specified will return the ``swidth`` value (in bytes) |
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in ``st_blksize``. If the filesystem does not have a ``swidth`` |
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specified but does specify an ``allocsize`` then ``allocsize`` |
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(in bytes) will be returned instead. Otherwise the behaviour |
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is the same as if ``nolargeio`` was specified. |
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logbufs=value |
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Set the number of in-memory log buffers. Valid numbers |
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range from 2-8 inclusive. |
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The default value is 8 buffers. |
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If the memory cost of 8 log buffers is too high on small |
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systems, then it may be reduced at some cost to performance |
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on metadata intensive workloads. The ``logbsize`` option below |
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controls the size of each buffer and so is also relevant to |
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this case. |
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logbsize=value |
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Set the size of each in-memory log buffer. The size may be |
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specified in bytes, or in kilobytes with a "k" suffix. |
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Valid sizes for version 1 and version 2 logs are 16384 (16k) |
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and 32768 (32k). Valid sizes for version 2 logs also |
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include 65536 (64k), 131072 (128k) and 262144 (256k). The |
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logbsize must be an integer multiple of the log |
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stripe unit configured at **mkfs(8)** time. |
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The default value for version 1 logs is 32768, while the |
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default value for version 2 logs is MAX(32768, log_sunit). |
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logdev=device and rtdev=device |
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Use an external log (metadata journal) and/or real-time device. |
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An XFS filesystem has up to three parts: a data section, a log |
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section, and a real-time section. The real-time section is |
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optional, and the log section can be separate from the data |
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section or contained within it. |
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noalign |
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Data allocations will not be aligned at stripe unit |
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boundaries. This is only relevant to filesystems created |
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with non-zero data alignment parameters (``sunit``, ``swidth``) by |
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**mkfs(8)**. |
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norecovery |
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The filesystem will be mounted without running log recovery. |
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If the filesystem was not cleanly unmounted, it is likely to |
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be inconsistent when mounted in ``norecovery`` mode. |
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Some files or directories may not be accessible because of this. |
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Filesystems mounted ``norecovery`` must be mounted read-only or |
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the mount will fail. |
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nouuid |
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Don't check for double mounted file systems using the file |
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system ``uuid``. This is useful to mount LVM snapshot volumes, |
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and often used in combination with ``norecovery`` for mounting |
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read-only snapshots. |
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noquota |
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Forcibly turns off all quota accounting and enforcement |
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within the filesystem. |
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uquota/usrquota/uqnoenforce/quota |
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User disk quota accounting enabled, and limits (optionally) |
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enforced. Refer to **xfs_quota(8)** for further details. |
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gquota/grpquota/gqnoenforce |
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Group disk quota accounting enabled and limits (optionally) |
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enforced. Refer to **xfs_quota(8)** for further details. |
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pquota/prjquota/pqnoenforce |
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Project disk quota accounting enabled and limits (optionally) |
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enforced. Refer to **xfs_quota(8)** for further details. |
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sunit=value and swidth=value |
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Used to specify the stripe unit and width for a RAID device |
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or a stripe volume. "value" must be specified in 512-byte |
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block units. These options are only relevant to filesystems |
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that were created with non-zero data alignment parameters. |
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The ``sunit`` and ``swidth`` parameters specified must be compatible |
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with the existing filesystem alignment characteristics. In |
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general, that means the only valid changes to ``sunit`` are |
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increasing it by a power-of-2 multiple. Valid ``swidth`` values |
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are any integer multiple of a valid ``sunit`` value. |
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Typically the only time these mount options are necessary if |
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after an underlying RAID device has had it's geometry |
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modified, such as adding a new disk to a RAID5 lun and |
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reshaping it. |
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swalloc |
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Data allocations will be rounded up to stripe width boundaries |
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when the current end of file is being extended and the file |
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size is larger than the stripe width size. |
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wsync |
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When specified, all filesystem namespace operations are |
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executed synchronously. This ensures that when the namespace |
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operation (create, unlink, etc) completes, the change to the |
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namespace is on stable storage. This is useful in HA setups |
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where failover must not result in clients seeing |
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inconsistent namespace presentation during or after a |
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failover event. |
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Deprecation of V4 Format |
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======================== |
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The V4 filesystem format lacks certain features that are supported by |
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the V5 format, such as metadata checksumming, strengthened metadata |
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verification, and the ability to store timestamps past the year 2038. |
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Because of this, the V4 format is deprecated. All users should upgrade |
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by backing up their files, reformatting, and restoring from the backup. |
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Administrators and users can detect a V4 filesystem by running xfs_info |
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against a filesystem mountpoint and checking for a string containing |
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"crc=". If no such string is found, please upgrade xfsprogs to the |
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latest version and try again. |
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The deprecation will take place in two parts. Support for mounting V4 |
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filesystems can now be disabled at kernel build time via Kconfig option. |
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The option will default to yes until September 2025, at which time it |
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will be changed to default to no. In September 2030, support will be |
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removed from the codebase entirely. |
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Note: Distributors may choose to withdraw V4 format support earlier than |
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the dates listed above. |
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Deprecated Mount Options |
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======================== |
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=========================== ================ |
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Name Removal Schedule |
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=========================== ================ |
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Mounting with V4 filesystem September 2030 |
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ikeep/noikeep September 2025 |
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attr2/noattr2 September 2025 |
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=========================== ================ |
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Removed Mount Options |
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===================== |
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=========================== ======= |
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Name Removed |
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=========================== ======= |
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delaylog/nodelaylog v4.0 |
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ihashsize v4.0 |
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irixsgid v4.0 |
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osyncisdsync/osyncisosync v4.0 |
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barrier v4.19 |
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nobarrier v4.19 |
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=========================== ======= |
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sysctls |
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======= |
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The following sysctls are available for the XFS filesystem: |
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fs.xfs.stats_clear (Min: 0 Default: 0 Max: 1) |
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Setting this to "1" clears accumulated XFS statistics |
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in /proc/fs/xfs/stat. It then immediately resets to "0". |
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fs.xfs.xfssyncd_centisecs (Min: 100 Default: 3000 Max: 720000) |
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The interval at which the filesystem flushes metadata |
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out to disk and runs internal cache cleanup routines. |
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fs.xfs.filestream_centisecs (Min: 1 Default: 3000 Max: 360000) |
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The interval at which the filesystem ages filestreams cache |
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references and returns timed-out AGs back to the free stream |
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pool. |
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fs.xfs.speculative_prealloc_lifetime |
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(Units: seconds Min: 1 Default: 300 Max: 86400) |
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The interval at which the background scanning for inodes |
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with unused speculative preallocation runs. The scan |
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removes unused preallocation from clean inodes and releases |
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the unused space back to the free pool. |
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fs.xfs.speculative_cow_prealloc_lifetime |
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This is an alias for speculative_prealloc_lifetime. |
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fs.xfs.error_level (Min: 0 Default: 3 Max: 11) |
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A volume knob for error reporting when internal errors occur. |
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This will generate detailed messages & backtraces for filesystem |
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shutdowns, for example. Current threshold values are: |
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XFS_ERRLEVEL_OFF: 0 |
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XFS_ERRLEVEL_LOW: 1 |
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XFS_ERRLEVEL_HIGH: 5 |
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fs.xfs.panic_mask (Min: 0 Default: 0 Max: 256) |
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Causes certain error conditions to call BUG(). Value is a bitmask; |
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OR together the tags which represent errors which should cause panics: |
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XFS_NO_PTAG 0 |
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XFS_PTAG_IFLUSH 0x00000001 |
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XFS_PTAG_LOGRES 0x00000002 |
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XFS_PTAG_AILDELETE 0x00000004 |
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XFS_PTAG_ERROR_REPORT 0x00000008 |
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XFS_PTAG_SHUTDOWN_CORRUPT 0x00000010 |
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XFS_PTAG_SHUTDOWN_IOERROR 0x00000020 |
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XFS_PTAG_SHUTDOWN_LOGERROR 0x00000040 |
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XFS_PTAG_FSBLOCK_ZERO 0x00000080 |
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XFS_PTAG_VERIFIER_ERROR 0x00000100 |
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This option is intended for debugging only. |
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fs.xfs.irix_symlink_mode (Min: 0 Default: 0 Max: 1) |
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Controls whether symlinks are created with mode 0777 (default) |
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or whether their mode is affected by the umask (irix mode). |
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fs.xfs.irix_sgid_inherit (Min: 0 Default: 0 Max: 1) |
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Controls files created in SGID directories. |
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If the group ID of the new file does not match the effective group |
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ID or one of the supplementary group IDs of the parent dir, the |
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ISGID bit is cleared if the irix_sgid_inherit compatibility sysctl |
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is set. |
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fs.xfs.inherit_sync (Min: 0 Default: 1 Max: 1) |
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Setting this to "1" will cause the "sync" flag set |
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by the **xfs_io(8)** chattr command on a directory to be |
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inherited by files in that directory. |
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fs.xfs.inherit_nodump (Min: 0 Default: 1 Max: 1) |
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Setting this to "1" will cause the "nodump" flag set |
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by the **xfs_io(8)** chattr command on a directory to be |
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inherited by files in that directory. |
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fs.xfs.inherit_noatime (Min: 0 Default: 1 Max: 1) |
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Setting this to "1" will cause the "noatime" flag set |
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by the **xfs_io(8)** chattr command on a directory to be |
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inherited by files in that directory. |
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fs.xfs.inherit_nosymlinks (Min: 0 Default: 1 Max: 1) |
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Setting this to "1" will cause the "nosymlinks" flag set |
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by the **xfs_io(8)** chattr command on a directory to be |
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inherited by files in that directory. |
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fs.xfs.inherit_nodefrag (Min: 0 Default: 1 Max: 1) |
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Setting this to "1" will cause the "nodefrag" flag set |
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by the **xfs_io(8)** chattr command on a directory to be |
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inherited by files in that directory. |
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fs.xfs.rotorstep (Min: 1 Default: 1 Max: 256) |
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In "inode32" allocation mode, this option determines how many |
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files the allocator attempts to allocate in the same allocation |
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group before moving to the next allocation group. The intent |
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is to control the rate at which the allocator moves between |
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allocation groups when allocating extents for new files. |
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Deprecated Sysctls |
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================== |
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=========================================== ================ |
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Name Removal Schedule |
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=========================================== ================ |
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fs.xfs.irix_sgid_inherit September 2025 |
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fs.xfs.irix_symlink_mode September 2025 |
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fs.xfs.speculative_cow_prealloc_lifetime September 2025 |
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=========================================== ================ |
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Removed Sysctls |
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=============== |
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============================= ======= |
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Name Removed |
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============================= ======= |
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fs.xfs.xfsbufd_centisec v4.0 |
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fs.xfs.age_buffer_centisecs v4.0 |
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============================= ======= |
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Error handling |
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============== |
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XFS can act differently according to the type of error found during its |
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operation. The implementation introduces the following concepts to the error |
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handler: |
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-failure speed: |
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Defines how fast XFS should propagate an error upwards when a specific |
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error is found during the filesystem operation. It can propagate |
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immediately, after a defined number of retries, after a set time period, |
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or simply retry forever. |
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-error classes: |
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Specifies the subsystem the error configuration will apply to, such as |
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metadata IO or memory allocation. Different subsystems will have |
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different error handlers for which behaviour can be configured. |
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-error handlers: |
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Defines the behavior for a specific error. |
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The filesystem behavior during an error can be set via ``sysfs`` files. Each |
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error handler works independently - the first condition met by an error handler |
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for a specific class will cause the error to be propagated rather than reset and |
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retried. |
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The action taken by the filesystem when the error is propagated is context |
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dependent - it may cause a shut down in the case of an unrecoverable error, |
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it may be reported back to userspace, or it may even be ignored because |
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there's nothing useful we can with the error or anyone we can report it to (e.g. |
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during unmount). |
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The configuration files are organized into the following hierarchy for each |
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mounted filesystem: |
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/sys/fs/xfs/<dev>/error/<class>/<error>/ |
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Where: |
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<dev> |
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The short device name of the mounted filesystem. This is the same device |
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name that shows up in XFS kernel error messages as "XFS(<dev>): ..." |
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<class> |
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The subsystem the error configuration belongs to. As of 4.9, the defined |
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classes are: |
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- "metadata": applies metadata buffer write IO |
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<error> |
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The individual error handler configurations. |
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Each filesystem has "global" error configuration options defined in their top |
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level directory: |
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/sys/fs/xfs/<dev>/error/ |
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fail_at_unmount (Min: 0 Default: 1 Max: 1) |
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Defines the filesystem error behavior at unmount time. |
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If set to a value of 1, XFS will override all other error configurations |
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during unmount and replace them with "immediate fail" characteristics. |
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i.e. no retries, no retry timeout. This will always allow unmount to |
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succeed when there are persistent errors present. |
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If set to 0, the configured retry behaviour will continue until all |
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retries and/or timeouts have been exhausted. This will delay unmount |
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completion when there are persistent errors, and it may prevent the |
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filesystem from ever unmounting fully in the case of "retry forever" |
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handler configurations. |
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Note: there is no guarantee that fail_at_unmount can be set while an |
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unmount is in progress. It is possible that the ``sysfs`` entries are |
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removed by the unmounting filesystem before a "retry forever" error |
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handler configuration causes unmount to hang, and hence the filesystem |
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must be configured appropriately before unmount begins to prevent |
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unmount hangs. |
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Each filesystem has specific error class handlers that define the error |
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propagation behaviour for specific errors. There is also a "default" error |
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handler defined, which defines the behaviour for all errors that don't have |
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specific handlers defined. Where multiple retry constraints are configured for |
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a single error, the first retry configuration that expires will cause the error |
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to be propagated. The handler configurations are found in the directory: |
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/sys/fs/xfs/<dev>/error/<class>/<error>/ |
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max_retries (Min: -1 Default: Varies Max: INTMAX) |
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Defines the allowed number of retries of a specific error before |
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the filesystem will propagate the error. The retry count for a given |
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error context (e.g. a specific metadata buffer) is reset every time |
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there is a successful completion of the operation. |
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Setting the value to "-1" will cause XFS to retry forever for this |
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specific error. |
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Setting the value to "0" will cause XFS to fail immediately when the |
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specific error is reported. |
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Setting the value to "N" (where 0 < N < Max) will make XFS retry the |
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operation "N" times before propagating the error. |
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retry_timeout_seconds (Min: -1 Default: Varies Max: 1 day) |
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Define the amount of time (in seconds) that the filesystem is |
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allowed to retry its operations when the specific error is |
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found. |
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Setting the value to "-1" will allow XFS to retry forever for this |
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specific error. |
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Setting the value to "0" will cause XFS to fail immediately when the |
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specific error is reported. |
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Setting the value to "N" (where 0 < N < Max) will allow XFS to retry the |
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operation for up to "N" seconds before propagating the error. |
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**Note:** The default behaviour for a specific error handler is dependent on both |
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the class and error context. For example, the default values for |
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"metadata/ENODEV" are "0" rather than "-1" so that this error handler defaults |
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to "fail immediately" behaviour. This is done because ENODEV is a fatal, |
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unrecoverable error no matter how many times the metadata IO is retried. |
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Workqueue Concurrency |
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===================== |
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|
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XFS uses kernel workqueues to parallelize metadata update processes. This |
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enables it to take advantage of storage hardware that can service many IO |
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operations simultaneously. This interface exposes internal implementation |
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details of XFS, and as such is explicitly not part of any userspace API/ABI |
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guarantee the kernel may give userspace. These are undocumented features of |
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the generic workqueue implementation XFS uses for concurrency, and they are |
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provided here purely for diagnostic and tuning purposes and may change at any |
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time in the future. |
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The control knobs for a filesystem's workqueues are organized by task at hand |
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and the short name of the data device. They all can be found in: |
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/sys/bus/workqueue/devices/${task}!${device} |
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|
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================ =========== |
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Task Description |
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================ =========== |
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xfs_iwalk-$pid Inode scans of the entire filesystem. Currently limited to |
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mount time quotacheck. |
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xfs-blockgc Background garbage collection of disk space that have been |
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speculatively allocated beyond EOF or for staging copy on |
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write operations. |
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================ =========== |
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For example, the knobs for the quotacheck workqueue for /dev/nvme0n1 would be |
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found in /sys/bus/workqueue/devices/xfs_iwalk-1111!nvme0n1/. |
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The interesting knobs for XFS workqueues are as follows: |
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|
|
============ =========== |
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Knob Description |
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============ =========== |
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max_active Maximum number of background threads that can be started to |
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run the work. |
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cpumask CPUs upon which the threads are allowed to run. |
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nice Relative priority of scheduling the threads. These are the |
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same nice levels that can be applied to userspace processes. |
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============ ===========
|
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