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BTRFS-MOUNT(5) | Btrfs Manual | BTRFS-MOUNT(5) |
NAME¶
btrfs-mount - mount options and supported file attributes for the btrfs filesystemDESCRIPTION¶
This document describes mount options specific to the btrfs filesystem. Other generic mount options are available,and are described in the mount(8) manpage.MOUNT OPTIONS¶
alloc_start=bytesDebugging option to force all block allocations above a
certain byte threshold on each block device. The value is specified in bytes,
optionally with a K, M, or G suffix, case insensitive. Default is 1MB.
autodefrag
Disable/enable auto defragmentation. Auto defragmentation
detects small random writes into files and queue them up for the defrag
process. Works best for small files; Not well suited for large database
workloads.
check_int|check_int_data|check_int_print_mask=value
These debugging options control the behavior of the
integrity checking module (the BTRFS_FS_CHECK_INTEGRITY config option
required). check_int enables the integrity checker module, which
examines all block write requests to ensure on-disk consistency, at a large
memory and CPU cost. check_int_data includes extent data in the
integrity checks, and implies the check_int option.
check_int_print_mask takes a bitmask of BTRFSIC_PRINT_MASK_* values as
defined in fs/btrfs/check-integrity.c, to control the integrity checker
module behavior.
See comments at the top of fs/btrfs/check-integrity.c for more
info.
commit=seconds
Set the interval of periodic commit, 30 seconds by
default. Higher values defer data being synced to permanent storage with
obvious consequences when the system crashes. The upper bound is not forced,
but a warning is printed if it’s more than 300 seconds (5
minutes).
compress|compress=type|compress-force|compress-force=type
Control BTRFS file data compression. Type may be
specified as "zlib" "lzo" or "no" (for no
compression, used for remounting). If no type is specified, zlib is used. If
compress-force is specified, all files will be compressed, whether or not they
compress well. If compression is enabled, nodatacow and nodatasum are
disabled.
degraded
Allow mounts to continue with missing devices. A
read-write mount may fail with too many devices missing, for example if a
stripe member is completely missing.
device=devicepath
Specify a device during mount so that ioctls on the
control device can be avoided. Especially useful when trying to mount a
multi-device setup as root. May be specified multiple times for multiple
devices.
discard
Disable/enable discard mount option. Discard issues
frequent 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 significant performance impact. (The
fstrim command is also available to initiate batch trims from
userspace).
enospc_debug
Disable/enable debugging option to be more verbose in
some ENOSPC conditions.
fatal_errors=action
Action to take when encountering a fatal error.
"bug" - BUG() on a fatal error. This is the default.
"panic" - panic() on a fatal error.
flushoncommit
The flushoncommit mount option forces any data
dirtied by a write in a prior transaction to commit as part of the current
commit. This makes the committed state a fully consistent view of the file
system from the application’s perspective (i.e., it includes all
completed file system operations). This was previously the behavior only when
a snapshot is created.
inode_cache: Enable free inode number caching. Defaults to off due to an
overflow problem when the free space crcs don’t fit inside a single
page.
max_inline=bytes
Specify the maximum amount of space, in bytes, that can
be inlined in a metadata B-tree leaf. The value is specified in bytes,
optionally with a K, M, or G suffix, case insensitive. In practice, this value
is limited by the root sector size, with some space unavailable due to leaf
headers. For a 4k sectorsize, max inline data is ~3900 bytes.
metadata_ratio=value
Specify that 1 metadata chunk should be allocated after
every value data chunks. Off by default.
noacl
Enable/disable support for Posix Access Control Lists
(ACLs). See the acl(5) manual page for more information about
ACLs.
nobarrier
ensure that certain IOs make it through the device cache
and are on persistent storage. If disabled on a device with a volatile
(non-battery-backed) write-back cache, nobarrier option will lead to
filesystem corruption on a system crash or power loss.
nodatacow
Enable/disable data copy-on-write for newly created
files. Nodatacow implies nodatasum, and disables all compression.
nodatasum
Enable/disable data checksumming for newly created files.
Datasum implies datacow.
notreelog
Enable/disable the tree logging used for fsync and O_SYNC
writes.
recovery
Enable autorecovery attempts if a bad tree root is found
at mount time. Currently this scans a list of several previous tree roots and
tries to use the first readable.
rescan_uuid_tree
Force check and rebuild procedure of the UUID tree. This
should not normally be needed.
skip_balance
Skip automatic resume of interrupted balance operation
after mount. May be resumed with "btrfs balance resume."
nospace_cache
Disable freespace cache loading without clearing the
cache.
clear_cache
Force clearing and rebuilding of the disk space cache if
something has gone wrong.
ssd|nossd|ssd_spread
Options to control ssd allocation schemes. By default,
BTRFS will enable or disable ssd allocation heuristics depending on whether a
rotational or nonrotational disk is in use. The ssd and nossd options can
override this autodetection.
The ssd_spread mount option attempts to allocate into big chunks of unused
space, and may perform better on low-end ssds. ssd_spread implies ssd,
enabling all other ssd heuristics as well.
subvol=path
Mount subvolume at path rather than the root
subvolume. The path is relative to the top level subvolume.
subvolid=ID
Mount subvolume specified by an ID number rather than the
root subvolume. This allows mounting of subvolumes which are not in the root
of the mounted filesystem. You can use "btrfs subvolume list" to see
subvolume ID numbers.
subvolrootid=objectid (deprecated)
Mount subvolume specified by objectid rather than
the root subvolume. This allows mounting of subvolumes which are not in the
root of the mounted filesystem. You can use "btrfs subvolume show"
to see the object ID for a subvolume.
thread_pool=number
The number of worker threads to allocate. The default
number is equal to the number of CPUs + 2, or 8, whichever is smaller.
user_subvol_rm_allowed
Allow subvolumes to be deleted by a non-root user. Use
with caution.
FILE ATTRIBUTES¶
The btrfs filesystem supports setting the following file attributes the chattr(1) utility a — append only A — no atime updates c — compressed C — no copy on write d — no dump D — synchronous directory updates i — immutable S — synchronous updates X — no compression For descriptions of these attribute flags, please refer to the chattr(1) man page.SEE ALSO¶
chattr(1), mkfs.btrfs(8), mount(8), btrfs(8)11/22/2014 | Btrfs v3.17 |