Provided by: btrfs-tools_4.4-1_i386 bug

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

       start [options] <path>
           start the balance operation according to the specified filters, no
           filters will rewrite the entire filesystem. The process runs in the
           foreground.

           Options

           -d[<filters>]
               act on data block groups, see FILTERS section for details about
               filters

           -m[<filters>]
               act on metadata chunks, see FILTERS section for details about
               filters

           -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
               starting with kernel 4.5, the data chunks can be converted
               to/from the DUP profile on a single device.

       limit=<number>, limit=<range>
           Process only given number of chunks, after all filters are applied.
           This can be used to specifically target a chunk in connection with
           other filters (drange, vrange) or just simply limit the amount of
           work done by a single balance run.

           The argument may be a single value or a range. The single value N
           means at most N chunks, equivalent to ..N range syntax. Kernels
           prior to 4.4 accept only the single value format. The range minimum
           and maximum are inclusive.

       stripes=<range>
           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)