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BTRFS-BALANCE(8)                                     Btrfs Manual                                    BTRFS-BALANCE(8)



NAME
       btrfs-balance - balance block groups on a btrfs filesystem

SYNOPSIS
       btrfs balance <subcommand> <args>

DESCRIPTION
       The primary purpose of the balance feature is to spread block groups accross all devices so they match
       constraints defined by the respective profiles. See mkfs.btrfs(8) section PROFILES for more details. The scope
       of the balancing process can be further tuned by use of filters that can select the block groups to process.
       Balance works only on a mounted filesystem.

       The balance operation is cancellable by the user. The on-disk state of the filesystem is always consistent so
       an unexpected interruption (eg. system crash, reboot) does not corrupt the filesystem. The progress of the
       balance operation is temporarily stored and will be resumed upon mount, unless the mount option skip_balance
       is specified.

           Warning
           running balance without filters will take a lot of time as it basically rewrites the entire filesystem and
           needs to update all block pointers.

       The filters can be used to perform following actions:

       ·   convert block group profiles (filter convert)

       ·   make block group usage more compact (filter usage)

       ·   perform actions only on a given device (filters devid, drange)

       The filters can be applied to a combination of block group types (data, metadata, system). Note that changing
       system needs the force option.

           Note
           the balance operation needs enough work space, ie. space that is completely unused in the filesystem,
           otherwise this may lead to ENOSPC reports. See the section ENOSPC for more details.

COMPATIBILITY
           Note
           The balance subcommand also exists under the btrfs filesystem namespace. This still works for backward
           compatibility but is deprecated and should not be used anymore.

           Note
           A short syntax btrfs balance <path> works due to backward compatibility but is deprecated and should not
           be used anymore. Use btrfs balance start command instead.

SUBCOMMAND
       cancel <path>
           cancel running or paused balance

       pause <path>
           pause running balance operation, this will store the state of the balance progress and used filters to the
           filesystem

       resume <path>
           resume interrupted balance

           -s[<filters>]
               act on system chunks (requires -f), see FILTERS section for details about filters.

           -v
               be verbose and print balance filter arguments

           -f
               force reducing of metadata integrity, eg. when going from raid1 to single

       status [-v] <path>
           Show status of running or paused balance.

           If -v option is given, output will be verbose.

FILTERS
       From kernel 3.3 onwards, btrfs balance can limit its action to a subset of the full filesystem, and can be
       used to change the replication configuration (e.g. moving data from single to RAID1). This functionality is
       accessed through the -d, -m or -s options to btrfs balance start, which filter on data, metadata and system
       blocks respectively.

       A filter has the following stucture: type[=params][,type=...]

       The available types are:

       profiles=<profiles>
           Balances only block groups with the given profiles. Parameters are a list of profile names separated by
           "|" (pipe).

       usage=<percent>, usage=<range>
           Balances only block groups with usage under the given percentage. The value of 0 is allowed and will clean
           up completely unused block groups, this should not require any new work space allocated. You may want to
           use usage=0 in case balance is returnin ENOSPC and your filesystem is not too full.

           The argument may be a single value or a range. The single value N means at most N percent used, equivalent
           to ..N range syntax. Kernels prior to 4.4 accept only the single value format. The minimum range boundary
           is inclusive, maximum is exclusive.

       devid=<id>
           Balances only block groups which have at least one chunk on the given device. To list devices with ids use
           btrfs fi show.

       drange=<range>
           Balance only block groups which overlap with the given byte range on any device. Use in conjunction with
           devid to filter on a specific device. The parameter is a range specified as start..end.

       vrange=<range>
           Balance only block groups which overlap with the given byte range in the filesystem’s internal virtual
           address space. This is the address space that most reports from btrfs in the kernel log use. The parameter
           is a range specified as start..end.

       convert=<profile>
           Convert each selected block group to the given profile name identified by parameters.

               Note

           Balance only block groups which have the given number of stripes. The parameter is a range specified as
           start..end. Makes sense fo block group profiles that utilize striping, ie. RAID0/10/5/6. The range minimum
           and maximum are inclusive.

       soft
           Takes no parameters. Only has meaning when converting between profiles. When doing convert from one
           profile to another and soft mode is on, chunks that already have the target profile are left untouched.
           This is useful e.g. when half of the filesystem was converted earlier but got cancelled.

           The soft mode switch is (like every other filter) per-type. For example, this means that we can convert
           metadata chunks the "hard" way while converting data chunks selectively with soft switch.

       Profile names, used in profiles and convert are one of: raid0, raid1, raid10, raid5, raid6, dup, single. The
       mixed data/metadata profiles can be converted in the same way, but it’s conversion between mixed and non-mixed
       is not implemented. For the constraints of the profiles please refer to mkfs.btrfs(8), section PROFILES.

ENOSPC
       The way balance operates, it usually needs to temporarily create a new block group and move the old data
       there. For that it needs work space, otherwise it fails for ENOSPC reasons. This is not the same ENOSPC as if
       the free space is exhausted. This refers to the space on the level of block groups.

       The free work space can be calculated from the output of the btrfs filesystem show command:

              Label: 'BTRFS'  uuid: 8a9d72cd-ead3-469d-b371-9c7203276265
                      Total devices 2 FS bytes used 77.03GiB
                      devid    1 size 53.90GiB used 51.90GiB path /dev/sdc2
                      devid    2 size 53.90GiB used 51.90GiB path /dev/sde1

       size - used = free work space 53.90GiB - 51.90GiB = 2.00GiB

       An example of a filter that does not require workspace is usage=0. This will scan through all unused block
       groups of a given type and will reclaim the space. Ater that it might be possible to run other filters.

       CONVERSIONS ON MULTIPLE DEVICES

       Conversion to profiles based on striping (RAID0, RAID5/6) require the work space on each device. An
       interrupted balance may leave partially filled block groups that might consume the work space.

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

AVAILABILITY
       btrfs is part of btrfs-progs. Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for further details.

SEE ALSO
       mkfs.btrfs(8), btrfs-device(8)



Btrfs v4.4.1                                          11/05/2016                                     BTRFS-BALANCE(8)