BTRFS-DEVICE(8) BTRFS BTRFS-DEVICE(8)
NAME
btrfs-device - manage devices of btrfs filesystems
SYNOPSIS
btrfs device <subcommand> <args>
DESCRIPTION
The btrfs device command group is used to manage devices of the btrfs
filesystems.
DEVICE MANAGEMENT
SUBCOMMAND
add [-Kf] <device> [<device>...] <path>
Add device(s) to the filesystem identified by path.
If applicable, a whole device discard (TRIM) operation is per-
formed prior to adding the device. A device with existing
filesystem detected by blkid(8) will prevent device addition and
has to be forced. Alternatively the filesystem can be wiped from
the device using e.g. the wipefs(8) tool.
The operation is instant and does not affect existing data. The
operation merely adds the device to the filesystem structures
and creates some block groups headers.
Options
-K|--nodiscard
do not perform discard (TRIM) by default
-f|--force
force overwrite of existing filesystem on the given
disk(s)
--enqueue
wait if there's another exclusive operation running, oth-
erwise continue
remove [options] <device>|<devid> [<device>|<devid>...] <path>
Remove device(s) from a filesystem identified by <path>
Device removal must satisfy the profile constraints, otherwise
the command fails. The filesystem must be converted to pro-
file(s) that would allow the removal. This can typically happen
when going down from 2 devices to 1 and using the RAID1 profile.
See the section TYPICAL USECASES.
The operation can take long as it needs to move all data from
the device.
It is possible to delete the device that was used to mount the
filesystem. The device entry in the mount table will be replaced
by another device name with the lowest device id.
If the filesystem is mounted in degraded mode (-o degraded),
special term missing can be used for device. In that case, the
first device that is described by the filesystem metadata, but
not present at the mount time will be removed.
NOTE:
In most cases, there is only one missing device in degraded
mode, otherwise mount fails. If there are two or more devices
missing (e.g. possible in RAID6), you need specify missing as
many times as the number of missing devices to remove all of
them.
Options
--enqueue
wait if there's another exclusive operation running, oth-
erwise continue
delete <device>|<devid> [<device>|<devid>...] <path>
Alias of remove kept for backward compatibility
replace <command> [options] <path>
Alias of whole command group btrfs replace for convenience. See
btrfs-replace(8).
ready <device>
Wait until all devices of a multiple-device filesystem are
scanned and registered within the kernel module. This is to pro-
vide a way for automatic filesystem mounting tools to wait be-
fore the mount can start. The device scan is only one of the
preconditions and the mount can fail for other reasons. Normal
users usually do not need this command and may safely ignore it.
scan [options] [<device> [<device>...]]
Scan devices for a btrfs filesystem and register them with the
kernel module. This allows mounting multiple-device filesystem
by specifying just one from the whole group.
If no devices are passed, all block devices that blkid reports
to contain btrfs are scanned.
The options --all-devices or -d can be used as a fallback in
case blkid is not available. If used, behavior is the same as
if no devices are passed.
The command can be run repeatedly. Devices that have been al-
ready registered remain as such. Reloading the kernel module
will drop this information. There's an alternative way of mount-
ing multiple-device filesystem without the need for prior scan-
ning. See the mount option device.
Options
-d|--all-devices
Enumerate and register all devices, use as a fallback in
case blkid is not available.
-u|--forget
Unregister a given device or all stale devices if no path
is given, the device must be unmounted otherwise it's an
error.
stats [options] <path>|<device>
Read and print the device IO error statistics for all devices of
the given filesystem identified by path or for a single device>.
The filesystem must be mounted. See section *DEVICE STATS for
more information about the reported statistics and the meaning.
Options
-z|--reset
Print the stats and reset the values to zero afterwards.
-c|--check
Check if the stats are all zeros and return 0 if it is
so. Set bit 6 of the return code if any of the statistics
is no-zero. The error values is 65 if reading stats from
at least one device failed, otherwise it's 64.
-T Print stats in a tabular form, devices as rows and stats
as columns
usage [options] <path> [<path>...]::
Show detailed information about internal allocations on devices.
The level of detail can differ if the command is run under a
regular or the root user (due to use of restricted ioctls). The
first example below is for normal user (warning included) and
the next one with root on the same filesystem:
WARNING: cannot read detailed chunk info, per-device usage will not be shown, run as root
/dev/sdc1, ID: 1
Device size: 931.51GiB
Device slack: 0.00B
Unallocated: 931.51GiB
/dev/sdc1, ID: 1
Device size: 931.51GiB
Device slack: 0.00B
Data,single: 641.00GiB
Data,RAID0/3: 1.00GiB
Metadata,single: 19.00GiB
System,single: 32.00MiB
Unallocated: 271.48GiB
• Device size -- size of the device as seen by the filesystem
(may be different than actual device size)
• Device slack -- portion of device not used by the filesystem
but still available in the physical space provided by the de-
vice, e.g. after a device shrink
• Data,single, Metadata,single, System,single -- in general,
list of block group type (Data, Metadata, System) and profile
(single, RAID1, ...) allocated on the device
• Data,RAID0/3 -- in particular, striped profiles
RAID0/RAID10/RAID5/RAID6 with the number of devices on which
the stripes are allocated, multiple occurrences of the same
profile can appear in case a new device has been added and all
new available stripes have been used for writes
• Unallocated -- remaining space that the filesystem can still
use for new block groups
Options
-b|--raw
raw numbers in bytes, without the B suffix
-h|--human-readable
print human friendly numbers, base 1024, this is the de-
fault
-H print human friendly numbers, base 1000
--iec select the 1024 base for the following options, according
to the IEC standard
--si select the 1000 base for the following options, according
to the SI standard
-k|--kbytes
show sizes in KiB, or kB with --si
-m|--mbytes
show sizes in MiB, or MB with --si
-g|--gbytes
show sizes in GiB, or GB with --si
-t|--tbytes
show sizes in TiB, or TB with --si
If conflicting options are passed, the last one takes prece-
dence.
DEVICE STATS
The device stats keep persistent record of several error classes re-
lated to doing IO. The current values are printed at mount time and up-
dated during filesystem lifetime or from a scrub run.
$ btrfs device stats /dev/sda3
[/dev/sda3].write_io_errs 0
[/dev/sda3].read_io_errs 0
[/dev/sda3].flush_io_errs 0
[/dev/sda3].corruption_errs 0
[/dev/sda3].generation_errs 0
write_io_errs
Failed writes to the block devices, means that the layers be-
neath the filesystem were not able to satisfy the write request.
read_io_errors
Read request analogy to write_io_errs.
flush_io_errs
Number of failed writes with the FLUSH flag set. The flushing is
a method of forcing a particular order between write requests
and is crucial for implementing crash consistency. In case of
btrfs, all the metadata blocks must be permanently stored on the
block device before the superblock is written.
corruption_errs
A block checksum mismatched or a corrupted metadata header was
found.
generation_errs
The block generation does not match the expected value (e.g.
stored in the parent node).
Since kernel 5.14 the device stats are also available in textual form
in /sys/fs/btrfs/FSID/devinfo/DEVID/error_stats.
EXIT STATUS
btrfs device returns a zero exit status if it succeeds. Non zero is re-
turned in case of failure.
If the -c option is used, btrfs device stats will add 64 to the exit
status if any of the error counters is non-zero.
AVAILABILITY
btrfs is part of btrfs-progs. Please refer to the documentation at
https://btrfs.readthedocs.io or wiki http://btrfs.wiki.kernel.org for
further information.
SEE ALSO
btrfs-balance(8) btrfs-device(8), btrfs-replace(8), mkfs.btrfs(8),
6.2 Feb 28, 2023 BTRFS-DEVICE(8)
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