BTRFS-SCRUB(8) BTRFS BTRFS-SCRUB(8)
NAME
btrfs-scrub - scrub btrfs filesystem, verify block checksums
SYNOPSIS
btrfs scrub <subcommand> <args>
DESCRIPTION
Scrub is a pass over all filesystem data and metadata and verifying the
checksums. If a valid copy is available (replicated block group pro-
files) then the damaged one is repaired. All copies of the replicated
profiles are validated.
NOTE:
Scrub is not a filesystem checker (fsck) and does not verify nor re-
pair structural damage in the filesystem. It really only checks
checksums of data and tree blocks, it doesn't ensure the content of
tree blocks is valid and consistent. There's some validation per-
formed when metadata blocks are read from disk but it's not exten-
sive and cannot substitute full btrfs check run.
The user is supposed to run it manually or via a periodic system ser-
vice. The recommended period is a month but could be less. The esti-
mated device bandwidth utilization is about 80% on an idle filesystem.
The IO priority class is by default idle so background scrub should not
significantly interfere with normal filesystem operation. The IO sched-
uler set for the device(s) might not support the priority classes
though.
The scrubbing status is recorded in /var/lib/btrfs/ in textual files
named scrub.status.UUID for a filesystem identified by the given UUID.
(Progress state is communicated through a named pipe in file
scrub.progress.UUID in the same directory.) The status file is updated
every 5 seconds. A resumed scrub will continue from the last saved po-
sition.
Scrub can be started only on a mounted filesystem, though it's possible
to scrub only a selected device. See btrfs scrub start for more.
SUBCOMMAND
cancel <path>|<device>
If a scrub is running on the filesystem identified by path or
device, cancel it.
If a device is specified, the corresponding filesystem is found
and btrfs scrub cancel behaves as if it was called on that
filesystem. The progress is saved in the status file so btrfs
scrub resume can continue from the last position.
resume [-BdqrR] [-c <ioprio_class> -n <ioprio_classdata>] <path>|<de-
vice>
Resume a cancelled or interrupted scrub on the filesystem iden-
tified by path or on a given device. The starting point is read
from the status file if it exists.
This does not start a new scrub if the last scrub finished suc-
cessfully.
Options
see scrub start.
start [-BdqrRf] [-c <ioprio_class> -n <ioprio_classdata>] <path>|<de-
vice>
Start a scrub on all devices of the mounted filesystem identi-
fied by path or on a single device. If a scrub is already run-
ning, the new one will not start. A device of an unmounted
filesystem cannot be scrubbed this way.
Without options, scrub is started as a background process. The
automatic repairs of damaged copies is performed by default for
block group profiles with redundancy.
The default IO priority of scrub is the idle class. The priority
can be configured similar to the ionice(1) syntax using -c and
-n options. Note that not all IO schedulers honor the ionice
settings.
Options
-B do not background and print scrub statistics when fin-
ished
-d print separate statistics for each device of the filesys-
tem (-B only) at the end
-r run in read-only mode, do not attempt to correct any-
thing, can be run on a read-only filesystem
-R raw print mode, print full data instead of summary
-c <ioprio_class>
set IO priority class (see ionice(1) manpage)
-n <ioprio_classdata>
set IO priority classdata (see ionice(1) manpage)
-f force starting new scrub even if a scrub is already run-
ning, this can useful when scrub status file is damaged
and reports a running scrub although it is not, but
should not normally be necessary
-q (deprecated) alias for global -q option
status [options] <path>|<device>
Show status of a running scrub for the filesystem identified by
path or for the specified device.
If no scrub is running, show statistics of the last finished or
cancelled scrub for that filesystem or device.
Options
-d print separate statistics for each device of the filesys-
tem
-R print all raw statistics without postprocessing as re-
turned by the status ioctl
--raw print all numbers raw values in bytes without the B suf-
fix
--human-readable
print human friendly numbers, base 1024, this is the de-
fault
--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
--kbytes
show sizes in KiB, or kB with --si
--mbytes
show sizes in MiB, or MB with --si
--gbytes
show sizes in GiB, or GB with --si
--tbytes
show sizes in TiB, or TB with --si
EXIT STATUS
btrfs scrub returns a zero exit status if it succeeds. Non zero is re-
turned in case of failure:
1 scrub couldn't be performed
2 there is nothing to resume
3 scrub found uncorrectable errors
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
mkfs.btrfs(8), ionice(1)
6.2 Feb 28, 2023 BTRFS-SCRUB(8)
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