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https://github.com/kdave/btrfs-progs
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fe27c052cb
[BUG] There is a bug report that read-only scrub on a read-write fs still causes writes into the fs, and that will be caught if there is a read-only block device among the storage stack. This will cause a kernel warning on failed transaction commit: BTRFS info (device dm-3): first mount of filesystem e18f0c40-88de-413f-9d7e-dcc8136ad6dd BTRFS info (device dm-3): using crc32c (crc32c-intel) checksum algorithm BTRFS info (device dm-3): using free-space-tree BTRFS info (device dm-3): scrub: started on devid 1 Trying to write to read-only block-device md127 btrfs_dev_stat_inc_and_print: 362 callbacks suppressed BTRFS error (device dm-3): bdev /dev/mapper/data errs: wr 1, rd 0, flush 0, corrupt 0, gen 0 BTRFS error (device dm-3): bdev /dev/mapper/data errs: wr 2, rd 0, flush 0, corrupt 0, gen 0 BTRFS error (device dm-3): bdev /dev/mapper/data errs: wr 3, rd 0, flush 0, corrupt 0, gen 0 BTRFS error (device dm-3): bdev /dev/mapper/data errs: wr 4, rd 0, flush 0, corrupt 0, gen 0 BTRFS error (device dm-3): bdev /dev/mapper/data errs: wr 5, rd 0, flush 0, corrupt 0, gen 0 BTRFS error (device dm-3): bdev /dev/mapper/data errs: wr 6, rd 0, flush 0, corrupt 0, gen 0 BTRFS error (device dm-3): bdev /dev/mapper/data errs: wr 7, rd 0, flush 0, corrupt 0, gen 0 BTRFS error (device dm-3): bdev /dev/mapper/data errs: wr 8, rd 0, flush 0, corrupt 0, gen 0 BTRFS error (device dm-3): bdev /dev/mapper/data errs: wr 9, rd 0, flush 0, corrupt 0, gen 0 BTRFS error (device dm-3): bdev /dev/mapper/data errs: wr 10, rd 0, flush 0, corrupt 0, gen 0 BTRFS: error (device dm-3) in btrfs_commit_transaction:2523: errno=-5 IO failure (Error while writing out transaction) BTRFS info (device dm-3 state E): forced readonly BTRFS warning (device dm-3 state E): Skipping commit of aborted transaction. BTRFS error (device dm-3 state EA): Transaction aborted (error -5) BTRFS: error (device dm-3 state EA) in cleanup_transaction:2017: errno=-5 IO failure BTRFS warning (device dm-3 state EA): failed setting block group ro: -5 BTRFS info (device dm-3 state EA): scrub: not finished on devid 1 with status: -5 [CAUSE] The root cause is inside btrfs_inc_block_group_ro(), where we need to hold a transaction handle, to prevent the transaction to be committed, until we hold ro_block_group_mutex. This will cause an empty transaction by itself, thus even if we can mark the block group read-only without any extra workload, we still need to commit the new and empty transaction. Unfortunately this means RO scrub on RW filesystem will always cause the fs to be updated. [FIX] The best fix is to make btrfs to avoid empty commit transaction, but even with that done, read-only scrub on rw mount can still cause real metadata updates (e.g. allocate new chunks and update device error statistics). It will be very complex to make read-only scrub to be fully read-only on a read-write btrfs. Thankfully read-only scrub on read-write mount with read-only device in the storage stack is pretty rare, thus a documentation update should be enough. Issue: #934 Pull-request: #935 Signed-off-by: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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229 lines
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btrfs-scrub(8)
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==============
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SYNOPSIS
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--------
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**btrfs scrub** <subcommand> <args>
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DESCRIPTION
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-----------
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.. include:: ch-scrub-intro.rst
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SUBCOMMAND
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----------
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cancel <path>|<device>
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If a scrub is running on the filesystem identified by *path* or
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*device*, cancel it.
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If a *device* is specified, the corresponding filesystem is found and
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:command:`btrfs scrub cancel` behaves as if it was called on that filesystem.
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The progress is saved in the status file so :command:`btrfs scrub resume` can
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continue from the last position.
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.. _man-scrub-limit:
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limit [options] <path>
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Show or set scrub limits on devices of the given filesystem.
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``Options``
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-d|--devid DEVID
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select the device by DEVID to apply the limit
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-l|--limit SIZE
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set the limit of the device to SIZE (size units with suffix),
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or 0 to reset to *unlimited*
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-a|--all
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apply the limit to all devices
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--raw
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print all numbers raw values in bytes without the *B* suffix
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--human-readable
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print human friendly numbers, base 1024, this is the default
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--iec
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select the 1024 base for the following options, according to
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the IEC standard
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--si
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select the 1000 base for the following options, according to the SI standard
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--kbytes
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show sizes in KiB, or kB with --si
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--mbytes
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show sizes in MiB, or MB with --si
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--gbytes
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show sizes in GiB, or GB with --si
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--tbytes
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show sizes in TiB, or TB with --si
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resume [-BdqrR] <path>|<device>
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Resume a cancelled or interrupted scrub on the filesystem identified by
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*path* or on a given *device*. The starting point is read from the
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status file if it exists.
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This does not start a new scrub if the last scrub finished successfully.
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``Options``
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see :command:`scrub start`.
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.. _man-scrub-start:
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start [-BdrRf] <path>|<device>
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Start a scrub on all devices of the mounted filesystem identified by
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*path* or on a single *device*. If a scrub is already running, the new
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one will not start. A device of an unmounted filesystem cannot be
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scrubbed this way.
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Without options, scrub is started as a background process. The
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automatic repairs of damaged copies are performed by default for block
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group profiles with redundancy. No-repair can be enabled by option *-r*.
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``Options``
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-B
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do not background and print scrub statistics when finished
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-d
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print separate statistics for each device of the filesystem
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(*-B* only) at the end
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-r
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run in read-only mode, do not attempt to correct anything, can
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be run on a read-only filesystem
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Note that a read-only scrub on a read-write filesystem can
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still cause writes into the filesystem due to some internal
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limitations. Only a read-only scrub on a read-only filesystem
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can avoid writes from scrub.
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-R
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raw print mode, print full data instead of summary
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-f
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force starting new scrub even if a scrub is already running,
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this can useful when scrub status file is damaged and reports a
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running scrub although it is not, but should not normally be
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necessary
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``Deprecated options``
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-c <ioprio_class>
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set IO priority class (see :manref:`ionice(1)` manual page) if the IO
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scheduler configured for the device supports ionice. This is
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only supported by BFQ or Kyber but is *not* supported by
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mq-deadline. Please read the section about
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:docref:`IO limiting <btrfs-scrub:scrub-io-limiting>`.
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-n <ioprio_classdata>
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set IO priority classdata (see :manref:`ionice(1)` manpage)
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-q
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(deprecated) alias for global *-q* option
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status [options] <path>|<device>
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Show status of a running scrub for the filesystem identified by *path*
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or for the specified *device*.
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If no scrub is running, show statistics of the last finished or
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cancelled scrub for that filesystem or device.
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``Options``
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-d
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print separate statistics for each device of the filesystem
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-R
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print all raw statistics without postprocessing as returned by
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the status ioctl
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--raw
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print all numbers raw values in bytes without the *B* suffix
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--human-readable
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print human friendly numbers, base 1024, this is the default
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--iec
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select the 1024 base for the following options, according to
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the IEC standard
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--si
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select the 1000 base for the following options, according to the SI standard
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--kbytes
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show sizes in KiB, or kB with --si
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--mbytes
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show sizes in MiB, or MB with --si
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--gbytes
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show sizes in GiB, or GB with --si
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--tbytes
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show sizes in TiB, or TB with --si
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A status on a filesystem without any error looks like the following:
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.. code-block:: none
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# btrfs scrub start /
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# btrfs scrub status /
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UUID: 76fac721-2294-4f89-a1af-620cde7a1980
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Scrub started: Wed Apr 10 12:34:56 2023
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Status: running
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Duration: 0:00:05
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Time left: 0:00:05
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ETA: Wed Apr 10 12:35:01 2023
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Total to scrub: 28.32GiB
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Bytes scrubbed: 13.76GiB (48.59%)
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Rate: 2.75GiB/s
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Error summary: no errors found
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With some errors found:
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.. code-block:: none
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Error summary: csum=72
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Corrected: 2
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Uncorrectable: 72
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Unverified: 0
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* *Corrected* -- number of bad blocks that were repaired from another copy
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* *Uncorrectable* -- errors detected at read time but not possible to repair from other copy
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* *Unverified* -- transient errors, first read failed but a retry
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succeeded, may be affected by lower layers that group or split IO requests
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* *Error summary* -- followed by a more detailed list of errors found
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* *csum* -- checksum mismatch
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* *super* -- super block errors, unless the error is fixed
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immediately, the next commit will overwrite superblock
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* *verify* -- metadata block header errors
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* *read* -- blocks can't be read due to IO errors
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It's possible to set a per-device limit via file
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:file:`sysfs/fs/btrfs/FSID/devinfo/scrub_speed_max`. In that case
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the limit is printed on the *Rate:* line if option *-d* is specified,
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or without it on a single-device filesystem. Read more about tat in
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section about :docref:`scrub IO limiting <btrfs-scrub:scrub-io-limiting>`.
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.. code-block:: none
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Rate: 989.0MiB/s (limit 1.0G/s)
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On a multi-device filesystem with at least one device limit the
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overall stats cannot print the limit without *-d* so there's a not that
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some limits are set:
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.. code-block:: none
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Rate: 36.37MiB/s (some device limits set)
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EXIT STATUS
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-----------
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**btrfs scrub** returns a zero exit status if it succeeds. Non zero is
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returned in case of failure:
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1
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scrub couldn't be performed
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2
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there is nothing to resume
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3
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scrub found uncorrectable errors
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AVAILABILITY
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------------
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**btrfs** is part of btrfs-progs. Please refer to the documentation at
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`https://btrfs.readthedocs.io <https://btrfs.readthedocs.io>`_.
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SEE ALSO
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--------
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:doc:`mkfs.btrfs`
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