DESCRIPTION
-----------
*btrfs scrub* is used to scrub a btrfs filesystem, which will read all data
-and metadata blocks from all disks and verify checksums. Automatically repair
+and metadata blocks from all devices and verify checksums. Automatically repair
corrupted blocks if there's a correct copy available.
+NOTE: Scrub is not a filesystem checker (fsck) and does not verify nor repair
+structural damage in the filesystem.
+
+The user is supposed to run it manually or via a periodic system service. The
+recommended period is a month but could be less. The estimated 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 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 position.
+
SUBCOMMAND
----------
*cancel* <path>|<device>::
-If a scrub is running on the filesystem identified by 'path>' cancel it.
+If a scrub is running on the filesystem identified by 'path' cancel it.
+
-Progress is saved in the scrub progress file ('/var/lib/btrfs/scrub.status.UUID')
-and scrubbing can be resumed later using the *btrfs scrub resume* command.
If a 'device' is specified, the corresponding filesystem is found and
*btrfs scrub cancel* behaves as if it was called on that filesystem.
a single 'device'. If a scrub is already running, the new one fails.
+
Without options, scrub is started as a background process.
-Progress can be obtained with the *btrfs scrub status* command. Scrubbing
-involves reading all data from all disks and verifying checksums. Errors are
-corrected along the way if possible.
+
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.
-B::::
do not background and print scrub statistics when finished
-d::::
-print separate statistics for each device of the filesystem ('-B' only)
+print separate statistics for each device of the filesystem ('-B' only) at the end
-q::::
be quiet, omit error messages and statistics
-r::::
-read only mode, do not attempt to correct anything, can be run on a read-only
+run in read-only mode, do not attempt to correct anything, can be run on a read-only
filesystem
-R::::
print raw statistics per-device instead of a summary
set IO priority classdata (see `ionice`(1) manpage)
-f::::
force starting new scrub even if a scrub is already running,
-this is useful when scrub status file is damaged and reports a running
-scrub although it is not
+this can useful when scrub status file is damaged and reports a running
+scrub although it is not, but should not normally be necessary
*status* [-d] <path>|<device>::
Show status of a running scrub for the filesystem identified by 'path' or
EXIT STATUS
-----------
*btrfs scrub* returns a zero exit status if it succeeds. Non zero is
-returned in case of failure.
+returned in case of failure:
+
+1::::
+scrub couldn't be performed
+2::::
+there is nothing to resume
+3::::
+scrub found uncorrectable errors
AVAILABILITY
------------
SEE ALSO
--------
`mkfs.btrfs`(8),
+`ionice`(1)
projects / platform / upstream / btrfs-progs.git / blobdiff