btrfs-device

BTRFS-DEVICE(8) BTRFS BTRFS-DEVICE(8)

NAME

   btrfs-device - manage devices of btrfs filesystems

SYNOPSIS

   btrfs device <subcommand> <args>

DESCRIPTION

   The btrfs device command group is used to manage devices of the btrfs filesystems.

DEVICE MANAGEMENT SUBCOMMAND

   add [-Kf] <device> [<device>...] <path>
          Add device(s) to the filesystem identified by path.

          If applicable, a whole device discard (TRIM) operation is performed prior to adding the device. A device with existing filesystem detected by blkid(8)
          will prevent device addition and has to be forced. Alternatively the filesystem can be wiped from the device using e.g. the wipefs(8) tool.

          The operation is instant and does not affect existing data. The operation merely adds the device to the filesystem structures and creates  some  block
          groups headers.

          Options

          -K|--nodiscard
                 do not perform discard (TRIM) by default

          -f|--force
                 force overwrite of existing filesystem on the given disk(s)

          --enqueue
                 wait if there's another exclusive operation running, otherwise continue

   remove [options] <device>|<devid> [<device>|<devid>...] <path>
          Remove device(s) from a filesystem identified by <path>

          Device  removal must satisfy the profile constraints, otherwise the command fails. The filesystem must be converted to profile(s) that would allow the
          removal. This can typically happen when going down from 2 devices to 1 and using the RAID1 profile. See the section TYPICAL USECASES.

          The operation can take long as it needs to move all data from the device.

          It is possible to delete the device that was used to mount the filesystem. The device entry in the mount table will be replaced by another device name
          with the lowest device id.

          If  the  filesystem is mounted in degraded mode (-o degraded), special term missing can be used for device. In that case, the first device that is de‐
          scribed by the filesystem metadata, but not present at the mount time will be removed.

          NOTE:
             In most cases, there is only one missing device in degraded mode, otherwise mount fails. If there are two or more devices missing (e.g. possible in
             RAID6), you need specify missing as many times as the number of missing devices to remove all of them.

          Options

          --enqueue
                 wait if there's another exclusive operation running, otherwise continue

   delete <device>|<devid> [<device>|<devid>...] <path>
          Alias of remove kept for backward compatibility

   replace <command> [options] <path>
          Alias of whole command group btrfs replace for convenience. See btrfs-replace(8).

   ready <device>
          Wait  until  all  devices  of a multiple-device filesystem are scanned and registered within the kernel module. This is to provide a way for automatic
          filesystem mounting tools to wait before the mount can start. The device scan is only one of the preconditions and the mount can fail for  other  rea‐
          sons.  Normal users usually do not need this command and may safely ignore it.

   scan [options] [<device> [<device>...]]
          Scan  devices for a btrfs filesystem and register them with the kernel module.  This allows mounting multiple-device filesystem by specifying just one
          from the whole group.

          If no devices are passed, all block devices that blkid reports to contain btrfs are scanned.

          The options --all-devices or -d can be used as a fallback in case blkid is not available.  If used, behavior is the same as if no devices are passed.

          The command can be run repeatedly. Devices that have been already registered remain as such. Reloading the kernel module will drop  this  information.
          There's an alternative way of mounting multiple-device filesystem without the need for prior scanning. See the mount option device.

          Options

          -d|--all-devices
                 Enumerate and register all devices, use as a fallback in case blkid is not available.

          -u|--forget
                 Unregister a given device or all stale devices if no path is given, the device must be unmounted otherwise it's an error.

   stats [options] <path>|<device>
          Read  and print the device IO error statistics for all devices of the given filesystem identified by path or for a single device>. The filesystem must
          be mounted.  See section *DEVICE STATS for more information about the reported statistics and the meaning.

          Options

          -z|--reset
                 Print the stats and reset the values to zero afterwards.

          -c|--check
                 Check if the stats are all zeros and return 0 if it is so. Set bit 6 of the return code if any of the statistics is no-zero. The  error  values
                 is 65 if reading stats from at least one device failed, otherwise it's 64.

          -T     Print stats in a tabular form, devices as rows and stats as columns

   usage [options] <path> [<path>...]::
          Show detailed information about internal allocations on devices.

          The  level  of  detail can differ if the command is run under a regular or the root user (due to use of restricted ioctls). The first example below is
          for normal user (warning included) and the next one with root on the same filesystem:

             WARNING: cannot read detailed chunk info, per-device usage will not be shown, run as root
             /dev/sdc1, ID: 1
                Device size:           931.51GiB
                Device slack:              0.00B
                Unallocated:           931.51GiB

             /dev/sdc1, ID: 1
                Device size:           931.51GiB
                Device slack:              0.00B
                Data,single:           641.00GiB
                Data,RAID0/3:            1.00GiB
                Metadata,single:        19.00GiB
                System,single:          32.00MiB
                Unallocated:           271.48GiB

          • Device size -- size of the device as seen by the filesystem (may be different than actual device size)

          • Device slack -- portion of device not used by the filesystem but still available in the physical space provided by the device, e.g.  after a  device
            shrink

          • Data,single,  Metadata,single, System,single -- in general, list of block group type (Data, Metadata, System) and profile (single, RAID1, ...) allo‐
            cated on the device

          • Data,RAID0/3 -- in particular, striped profiles RAID0/RAID10/RAID5/RAID6 with the number of devices on which the stripes are allocated, multiple oc‐
            currences of the same profile can appear in case a new device has been added and all new available stripes have been used for writes

          • Unallocated -- remaining space that the filesystem can still use for new block groups

          Options

          -b|--raw
                 raw numbers in bytes, without the B suffix

          -h|--human-readable
                 print human friendly numbers, base 1024, this is the default

          -H     print human friendly numbers, base 1000

          --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

          -k|--kbytes
                 show sizes in KiB, or kB with --si

          -m|--mbytes
                 show sizes in MiB, or MB with --si

          -g|--gbytes
                 show sizes in GiB, or GB with --si

          -t|--tbytes
                 show sizes in TiB, or TB with --si

          If conflicting options are passed, the last one takes precedence.

DEVICE STATS

   The  device  stats  keep  persistent  record  of  several  error classes related to doing IO. The current values are printed at mount time and updated during
   filesystem lifetime or from a scrub run.

      $ btrfs device stats /dev/sda3
      [/dev/sda3].write_io_errs   0
      [/dev/sda3].read_io_errs    0
      [/dev/sda3].flush_io_errs   0
      [/dev/sda3].corruption_errs 0
      [/dev/sda3].generation_errs 0

   write_io_errs
          Failed writes to the block devices, means that the layers beneath the filesystem were not able to satisfy the write request.

   read_io_errors
          Read request analogy to write_io_errs.

   flush_io_errs
          Number of failed writes with the FLUSH flag set. The flushing is a method of forcing a particular order between write requests and is crucial for  im‐
          plementing  crash consistency. In case of btrfs, all the metadata blocks must be permanently stored on the block device before the superblock is writ‐
          ten.

   corruption_errs
          A block checksum mismatched or a corrupted metadata header was found.

   generation_errs
          The block generation does not match the expected value (e.g. stored in the parent node).

   Since kernel 5.14 the device stats are also available in textual form in /sys/fs/btrfs/FSID/devinfo/DEVID/error_stats.

EXIT STATUS

   btrfs device returns a zero exit status if it succeeds. Non zero is returned in case of failure.

   If the -c option is used, btrfs device stats will add 64 to the exit status if any of the error counters is non-zero.

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  informa‐
   tion.