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NAME | DESCRIPTION | OPERATIONS | MOUNT OPTIONS | REMOVED MOUNT OPTIONS | FILE ATTRIBUTES | SEE ALSO | COLOPHON |
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xfs(5) File Formats Manual xfs(5)
xfs - layout, mount options, and supported file attributes for the
XFS filesystem
An XFS filesystem can reside on a regular disk partition or on a
logical volume. An XFS filesystem has up to three parts: a data
section, a log section, and a realtime section. Using the default
mkfs.xfs(8) options, the realtime section is absent, and the log
area is contained within the data section. The log section can be
either separate from the data section or contained within it. The
filesystem sections are divided into a certain number of blocks,
whose size is specified at mkfs.xfs(8) time with the -b option.
The data section contains all the filesystem metadata (inodes,
directories, indirect blocks) as well as the user file data for
ordinary (non-realtime) files and the log area if the log is
internal to the data section. The data section is divided into a
number of allocation groups. The number and size of the
allocation groups are chosen by mkfs.xfs(8) so that there is
normally a small number of equal-sized groups. The number of
allocation groups controls the amount of parallelism available in
file and block allocation. It should be increased from the
default if there is sufficient memory and a lot of allocation
activity. The number of allocation groups should not be set very
high, since this can cause large amounts of CPU time to be used by
the filesystem, especially when the filesystem is nearly full.
More allocation groups are added (of the original size) when
xfs_growfs(8) is run.
The log section (or area, if it is internal to the data section)
is used to store changes to filesystem metadata while the
filesystem is running until those changes are made to the data
section. It is written sequentially during normal operation and
read only during mount. When mounting a filesystem after a crash,
the log is read to complete operations that were in progress at
the time of the crash.
The realtime section is used to store the data of realtime files.
These files had an attribute bit set through xfsctl(3) after file
creation, before any data was written to the file. The realtime
section is divided into a number of extents of fixed size
(specified at mkfs.xfs(8) time). Each file in the realtime
section has an extent size that is a multiple of the realtime
section extent size.
Each allocation group contains several data structures. The first
sector contains the superblock. For allocation groups after the
first, the superblock is just a copy and is not updated after
mkfs.xfs(8). The next three sectors contain information for block
and inode allocation within the allocation group. Also contained
within each allocation group are data structures to locate free
blocks and inodes; these are located through the header
structures.
Each XFS filesystem is labeled with a Universal Unique Identifier
(UUID). The UUID is stored in every allocation group header and
is used to help distinguish one XFS filesystem from another,
therefore you should avoid using dd(1) or other block-by-block
copying programs to copy XFS filesystems. If two XFS filesystems
on the same machine have the same UUID, xfsdump(8) may become
confused when doing incremental and resumed dumps. xfsdump(8) and
xfsrestore(8) are recommended for making copies of XFS
filesystems. To mount a snapshot of an already-mounted
filesystem, you may need to supply the nouuid option to mount (8).
Some functionality specific to the XFS filesystem is accessible to
applications through the xfsctl(3) and by-handle (see
open_by_handle(3)) interfaces.
The following XFS-specific mount options may be used when mounting
an XFS filesystem. Other generic options may be used as well;
refer to the mount(8) manual page for more details.
allocsize=size
Sets the buffered I/O end-of-file preallocation size when
doing delayed allocation writeout. Valid values for this
option are page size (typically 4KiB) through to 1GiB,
inclusive, in power-of-2 increments.
The default behavior 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 behavior.
attr2|noattr2
Note: These options have been deprecated as of kernel
v5.10; The noattr2 option will be removed no earlier than
in September 2025 and attr2 option will be immutable
default.
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 behavior is determined by the on-disk feature
bit indicating that attr2 behavior 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.
dax=value
Set CPU direct access (DAX) behavior for the current
filesystem. This mount option accepts the following values:
"dax=inode" DAX will be enabled only on regular files with
FS_XFLAG_DAX applied.
"dax=never" DAX will not be enabled for any files.
FS_XFLAG_DAX will be ignored.
"dax=always" DAX will be enabled for all regular files,
regardless of the FS_XFLAG_DAX state.
If no option is used when mounting a filesystem stored on a
DAX capable device, dax=inode will be used as default.
For details regarding DAX behavior in kernel, please refer
to kernel's documentation at filesystems/dax.txt
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. For this reason, nodiscard is the
default.
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
Note: These options have been deprecated as of kernel
v5.10; The noikeep option will be removed no earlier than
in September 2025 and ikeep option will be immutable
default.
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. noikeep is the default.
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.
For kernel v3.7 and later, inode64 is the default.
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 behavior is the same as if "nolargeio" was specified.
nolargeio is the default.
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 relevant to
this case.
logbsize=value
Set the size of each in-memory log buffer. The size may be
specified in bytes, or in kibibytes (KiB) with a "k"
suffix. Valid sizes for version 1 and version 2 logs are
16384 (value=16k) and 32768 (value=32k). Valid sizes for
version 2 logs also include 65536 (value=64k), 131072
(value=128k) and 262144 (value=256k). The logbsize must be
an integer multiple of the log stripe unit configured at
mkfs time.
The default value 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/quota/uqnoenforce/qnoenforce
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.
The following mount options have been removed from the kernel, and
will yield mount failures if specified. Mount options are
deprecated for a significant period time prior to removal.
Name Removed
---- -------
delaylog/nodelaylog v4.0
ihashsize v4.0
irixsgid v4.0
osyncisdsync/osyncisosync v4.0
barrier/nobarrier v4.19
The XFS filesystem supports setting the following file attributes
on Linux systems using the chattr(1) utility:
a - append only
A - no atime updates
d - no dump
i - immutable
S - synchronous updates
For descriptions of these attribute flags, please refer to the
chattr(1) man page.
chattr(1), xfsctl(3), mount(8), mkfs.xfs(8), xfs_info(8),
xfs_admin(8), xfsdump(8), xfsrestore(8).
This page is part of the xfsprogs (utilities for XFS filesystems)
project. Information about the project can be found at
⟨http://xfs.org/⟩. If you have a bug report for this manual page,
send it to linux-xfs@vger.kernel.org. This page was obtained from
the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/fs/xfs/xfsprogs-dev.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-06-23.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
xfs(5)
Pages that refer to this page: chattr(1), FS_IOC_SETFLAGS(2const), mount_setattr(2), handle(3), xfsctl(3), filesystems(5), dmstats(8), fsck.xfs(8), mount(8), systemd-makefs@.service(8), xfs_admin(8), xfs_bmap(8), xfs_copy(8), xfs_db(8), xfsdump(8), xfs_freeze(8), xfs_fsr(8), xfs_growfs(8), xfs_io(8), xfs_logprint(8), xfs_mdrestore(8), xfs_metadump(8), xfs_ncheck(8), xfs_quota(8), xfs_repair(8), xfs_rtcp(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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