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.
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.
attr2/noattr2
The options enable/disable (default is disabled for backward
compatibility on-disk) 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 (by setting or
removing extended attributes) the on-disk superblock feature
bit field will be updated to reflect this format being in use.
CRC enabled filesystems always use the attr2 format, and so
will reject the noattr2 mount option if it is set.
barrier
Enables the use of block layer write barriers for writes into
the journal and unwritten extent conversion. This allows for
drive level write caching to be enabled, for devices that
support write barriers.
discard
Issue command 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.
dmapi
Enable the DMAPI (Data Management API) event callouts.
Use with the “mtpt” option.
grpid/bsdgroups and 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 (the default) 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.
ihashsize=value
In memory inode hashes have been removed, so this option has
no function as of August 2007. Option is deprecated.
ikeep/noikeep
When ikeep is specified, XFS does not delete empty inode clusters
and keeps them around on disk. ikeep is the traditional XFS
behaviour. When noikeep is specified, empty inode clusters
are returned to the free space pool. The default is noikeep for
non-DMAPI mounts, while ikeep is the default when DMAPI is in use.
inode64
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. This is
the default allocation option. Applications which do not handle
inode numbers bigger than 32 bits, should use inode32 option.
inode32
Indicates that XFS is limited to create inodes at locations which
will not result in inode numbers with more than 32 bits of
significance. This is provided for backwards compatibility, since
64 bits inode numbers might cause problems for some applications
that cannot handle large inode numbers.
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.
If “largeio” specified, a filesystem that has 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.
If neither of these two options are specified, then filesystem
will behave 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 for filesystems with a
blocksize of 64KiB, 4 buffers for filesystems with a blocksize
of 32KiB, 3 buffers for filesystems with a blocksize of 16KiB
and 2 buffers for all other configurations. Increasing the
number of buffers may increase performance on some workloads
at the cost of the memory used for the additional log buffers
and their associated control structures.
logbsize=value
Set the size of each in-memory log buffer.
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 default value for machines with more than 32MiB of memory
is 32768, machines with less memory use 16384 by default.
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.
mtpt=mountpoint
Use with the “dmapi” option. The value specified here will be
included in the DMAPI mount event, and should be the path of
the actual mountpoint that is used.
noalign
Data allocations will not be aligned at stripe unit boundaries.
noatime
Access timestamps are not updated when a file is read.
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.
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.
If this option is not specified and the filesystem was made on
a stripe volume or the stripe width or unit were specified for
the RAID device at mkfs time, then the mount system call will
restore the value from the superblock. For filesystems that
are made directly on RAID devices, these options can be used
to override the information in the superblock if the underlying
disk layout changes after the filesystem has been created.
The “swidth” option is required if the “sunit” option has been
specified, and must be a multiple of the “sunit” value.
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.
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 xfssyncd thread flushes metadata
out to disk. This thread will flush log activity out, and
do some processing on unlinked inodes.
fs.xfs.xfsbufd_centisecs (Min: 50 Default: 100 Max: 3000)
The interval at which xfsbufd scans the dirty metadata buffers list.
fs.xfs.age_buffer_centisecs (Min: 100 Default: 1500 Max: 720000)
The age at which xfsbufd flushes dirty metadata buffers to disk.
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.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.
Error handling
XFS can act differently according to the type of error found during its
operation. The implementation introduces the following concepts to the error
handler:
-failure speed:
Defines how fast XFS should propagate an error upwards when a specific
error is found during the filesystem operation. It can propagate
immediately, after a defined number of retries, after a set time period,
or simply retry forever.
-error classes:
Specifies the subsystem the error configuration will apply to, such as
metadata IO or memory allocation. Different subsystems will have
different error handlers for which behaviour can be configured.
-error handlers:
Defines the behavior for a specific error.
The filesystem behavior during an error can be set via sysfs files. Each
error handler works independently - the first condition met by an error handler
for a specific class will cause the error to be propagated rather than reset and
retried.
The action taken by the filesystem when the error is propagated is context
dependent - it may cause a shut down in the case of an unrecoverable error,
it may be reported back to userspace, or it may even be ignored because
there’s nothing useful we can with the error or anyone we can report it to (e.g.
during unmount).
The configuration files are organized into the following hierarchy for each
mounted filesystem:
/sys/fs/xfs/
Where:
The short device name of the mounted filesystem. This is the same device
name that shows up in XFS kernel error messages as “XFS(
- "metadata": applies metadata buffer write IO
Each filesystem has “global” error configuration options defined in their top
level directory:
/sys/fs/xfs/
fail_at_unmount (Min: 0 Default: 1 Max: 1)
Defines the filesystem error behavior at unmount time.
If set to a value of 1, XFS will override all other error configurations
during unmount and replace them with "immediate fail" characteristics.
i.e. no retries, no retry timeout. This will always allow unmount to
succeed when there are persistent errors present.
If set to 0, the configured retry behaviour will continue until all
retries and/or timeouts have been exhausted. This will delay unmount
completion when there are persistent errors, and it may prevent the
filesystem from ever unmounting fully in the case of "retry forever"
handler configurations.
Note: there is no guarantee that fail_at_unmount can be set whilst an
unmount is in progress. It is possible that the sysfs entries are
removed by the unmounting filesystem before a "retry forever" error
handler configuration causes unmount to hang, and hence the filesystem
must be configured appropriately before unmount begins to prevent
unmount hangs.
Each filesystem has specific error class handlers that define the error
propagation behaviour for specific errors. There is also a “default” error
handler defined, which defines the behaviour for all errors that don’t have
specific handlers defined. Where multiple retry constraints are configuredi for
a single error, the first retry configuration that expires will cause the error
to be propagated. The handler configurations are found in the directory:
/sys/fs/xfs/
max_retries (Min: -1 Default: Varies Max: INTMAX)
Defines the allowed number of retries of a specific error before
the filesystem will propagate the error. The retry count for a given
error context (e.g. a specific metadata buffer) is reset every time
there is a successful completion of the operation.
Setting the value to "-1" will cause XFS to retry forever for this
specific error.
Setting the value to "0" will cause XFS to fail immediately when the
specific error is reported.
Setting the value to "N" (where 0 < N < Max) will make XFS retry the
operation "N" times before propagating the error.
retry_timeout_seconds (Min: -1 Default: Varies Max: 1 day)
Define the amount of time (in seconds) that the filesystem is
allowed to retry its operations when the specific error is
found.
Setting the value to "-1" will allow XFS to retry forever for this
specific error.
Setting the value to "0" will cause XFS to fail immediately when the
specific error is reported.
Setting the value to "N" (where 0 < N < Max) will allow XFS to retry the
operation for up to "N" seconds before propagating the error.
Note: The default behaviour for a specific error handler is dependent on both
the class and error context. For example, the default values for
“metadata/ENODEV” are “0” rather than “-1” so that this error handler defaults
to “fail immediately” behaviour. This is done because ENODEV is a fatal,
unrecoverable error no matter how many times the metadata IO is retried.
