29 lines
1.5 KiB
ReStructuredText
29 lines
1.5 KiB
ReStructuredText
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Scrub is a pass over all filesystem data and metadata and verifying the
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checksums. If a valid copy is available (replicated block group profiles) then
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the damaged one is repaired. All copies of the replicated profiles are validated.
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.. note::
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Scrub is not a filesystem checker (fsck) and does not verify nor repair
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structural damage in the filesystem. It really only checks checksums of data
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and tree blocks, it doesn't ensure the content of tree blocks is valid and
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consistent. There's some validation performed when metadata blocks are read
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from disk but it's not extensive and cannot substitute full *btrfs check*
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run.
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The user is supposed to run it manually or via a periodic system service. The
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recommended period is a month but could be less. The estimated device bandwidth
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utilization is about 80% on an idle filesystem. The IO priority class is by
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default *idle* so background scrub should not significantly interfere with
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normal filesystem operation. The IO scheduler set for the device(s) might not
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support the priority classes though.
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The scrubbing status is recorded in */var/lib/btrfs/* in textual files named
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*scrub.status.UUID* for a filesystem identified by the given UUID. (Progress
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state is communicated through a named pipe in file *scrub.progress.UUID* in the
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same directory.) The status file is updated every 5 seconds. A resumed scrub
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will continue from the last saved position.
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Scrub can be started only on a mounted filesystem, though it's possible to
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scrub only a selected device. See **btrfs scrub start** for more.
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