[PATCH 01/17] xfs: update mount options documentation

Dave Chinner
2013-06-07T05:46:00Z

Because it's horribly out of date.

And mark various deprecated options as deprecated and give them a
removal date.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
Documentation/filesystems/xfs.txt | 282 +++++++++++++++++++++++++------------
1 file changed, 192 insertions(+), 90 deletions(-)

diff --git a/Documentation/filesystems/xfs.txt b/Documentation/filesystems/xfs.txt
index 83577f0..28afbd1 100644
--- a/Documentation/filesystems/xfs.txt
+++ b/Documentation/filesystems/xfs.txt
@@ -25,6 +25,13 @@ When mounting an XFS filesystem, the following options are accepted.
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 (default is disabled for backward
compatibility on-disk) an "opportunistic" improvement to be
@@ -36,86 +43,108 @@ When mounting an XFS filesystem, the following options are accepted.
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.
+ 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
- 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.
+ The default behaviour is to enable barriers.

- dmapi
- Enable the DMAPI (Data Management API) event callouts.
- Use with the "mtpt" option.
+ discard/nodiscard

- 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.
+ 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.

- ihashsize=value
- In memory inode hashes have been removed, so this option has
- no function as of August 2007. Option is deprecated.
+ The default behaviour is disable discard commands.
+
+ 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 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.
+
+ 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. 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.
+ 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.
+
+ The default behaviour is delete inode clusters (noikeep).

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.
+ 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. Applications which do
+ not handle inode numbers bigger than 32 bits should use
+ inode32 option.
+
+ This is the default allocation behaviour, even on 32 bit
+ machines when neither inode64 or inode32 is specified.

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.
+ 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. This 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.

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.
+ 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.
+
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.
+ 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.

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.
+ 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
+ version 2 log size 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.
@@ -124,16 +153,12 @@ When mounting an XFS filesystem, the following options are accepted.
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.
+ 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.
@@ -144,8 +169,14 @@ When mounting an XFS filesystem, the following options are accepted.
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.
+ 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)
@@ -160,24 +191,68 @@ When mounting an XFS filesystem, the following options are accepted.
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.
+ 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. If
+ the filesystem was not created with data alignment
+ constraints, then it may be impossible to set a valid sunit
+ (and hence swidth) value. 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.
+
+ For filesystems that have existing data alignment values on
+ disk (i.e. specified by mkfs), any new valid values passed
+ in as mount options will overwrite the values stored on
+ disk. Hence this mount option does not need to be specified
+ for every mount operation in this case.

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
=======
@@ -189,15 +264,20 @@ The following sysctls are available for the XFS filesystem:
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.
+ The interval at which the filesystem flushes metadata
+ out to disk and runs internal cache cleanup routines.

- fs.xfs.xfsbufd_centisecs (Min: 50 Default: 100 Max: 3000)
- The interval at which xfsbufd scans the dirty metadata buffers list.
+ 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.age_buffer_centisecs (Min: 100 Default: 1500 Max: 720000)
- The age at which xfsbufd flushes dirty metadata buffers to disk.
+ 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 at. 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.
@@ -254,9 +334,31 @@ The following sysctls are available for the XFS filesystem:
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.