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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.
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) utilitySEE ALSO¶
chattr(1), mkfs.btrfs(8), mount(8), btrfs(8)06/20/2015 | Btrfs v3.17 |