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-rw-r--r-- | Documentation/btrfs-scrub.asciidoc | 32 |
1 files changed, 22 insertions, 10 deletions
diff --git a/Documentation/btrfs-scrub.asciidoc b/Documentation/btrfs-scrub.asciidoc index 83ddcaa7..40e793c2 100644 --- a/Documentation/btrfs-scrub.asciidoc +++ b/Documentation/btrfs-scrub.asciidoc @@ -12,16 +12,30 @@ SYNOPSIS 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 filesytem. The IO priority class is by +default 'idle' so background scrub should not interfere with normal filesystem +operation significantly. + +The scrubbing status is recorded in '/var/lib/btrfs/' in textual files named +'scrub.status.UUID' for a filesystem identified by the given UUID. (An +itermediate progress is communicated through a named pipe in file +'scrub.progress.UUID' in the same directory.) The status file is updated +periodically every 5 seconds. An 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. + -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. @@ -40,9 +54,6 @@ Start a scrub on all devices of the filesystem identified by 'path' or on 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. @@ -52,11 +63,11 @@ 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 @@ -66,8 +77,8 @@ set IO priority class (see `ionice`(1) manpage) 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 @@ -95,3 +106,4 @@ further details. SEE ALSO -------- `mkfs.btrfs`(8), +`ionice`(1) |