BTRFS-QGROUP(8)



BTRFS-QGROUP(8)                  Btrfs Manual                  BTRFS-QGROUP(8)

NAME
       btrfs-qgroup - control the quota group of a btrfs filesystem

SYNOPSIS
       btrfs qgroup <subcommand> <args>

DESCRIPTION
       btrfs qgroup is used to control quota group (qgroup) of a btrfs
       filesystem.

           Note
           To use qgroup you need to enable quota first using btrfs quota
           enable command.

           Warning
           Qgroup is not stable yet and will impact performance in current
           mainline kernel (v4.14).

QGROUP
       Quota groups or qgroup in btrfs make a tree hierarchy, the leaf qgroups
       are attached to subvolumes. The size limits are set per qgroup and
       apply when any limit is reached in tree that contains a given
       subvolume.

       The limits are separated between shared and exclusive and reflect the
       extent ownership. For example a fresh snapshot shares almost all the
       blocks with the original subvolume, new writes to either subvolume will
       raise towards the exclusive limit.

       The qgroup identifiers conform to level/id where level 0 is reserved to
       the qgroups associated with subvolumes. Such qgroups are created
       automatically.

       The qgroup hierarchy is built by commands create and assign.

           Note
           If the qgroup of a subvolume is destroyed, quota about the
           subvolume will not be functional until qgroup 0/<subvolume id> is
           created again.

SUBCOMMAND
       assign [options] <src> <dst> <path>
           Assign qgroup <src> as the child qgroup of <dst> in the btrfs
           filesystem identified by <path>.

           Options

           --rescan
               (default since: 4.19) Automatically schedule quota rescan if
               the new qgroup assignment would lead to quota inconsistency.
               See QUOTA RESCAN for more information.

           --no-rescan
               Explicitly ask not to do a rescan, even if the assignment will
               make the quotas inconsistent. This may be useful for repeated
               calls where the rescan would add unnecessary overhead.

       create <qgroupid> <path>
           Create a subvolume quota group.

           For the 0/<subvolume id> qgroup, a qgroup can be created even
           before the subvolume is created.

       destroy <qgroupid> <path>
           Destroy a qgroup.

           If a qgroup is not isolated, meaning it is a parent or child
           qgroup, then it can only be destroyed after the relationship is
           removed.

       limit [options] <size>|none [<qgroupid>] <path>
           Limit the size of a qgroup to <size> or no limit in the btrfs
           filesystem identified by <path>.

           If <qgroupid> is not given, qgroup of the subvolume identified by
           <path> is used if possible.

           Options

           -c
               limit amount of data after compression. This is the default, it
               is currently not possible to turn off this option.

           -e
               limit space exclusively assigned to this qgroup.

       remove <src> <dst> <path>
           Remove the relationship between child qgroup <src> and parent
           qgroup <dst> in the btrfs filesystem identified by <path>.

           Options

           --rescan
               (default since: 4.19) Automatically schedule quota rescan if
               the removed qgroup relation would lead to quota inconsistency.
               See QUOTA RESCAN for more information.

           --no-rescan
               Explicitly ask not to do a rescan, even if the removal will
               make the quotas inconsistent. This may be useful for repeated
               calls where the rescan would add unnecessary overhead.

       show [options] <path>
           Show all qgroups in the btrfs filesystem identified by <path>.

           Options

           -p
               print parent qgroup id.

           -c
               print child qgroup id.

           -r
               print limit of referenced size of qgroup.

           -e
               print limit of exclusive size of qgroup.

           -F
               list all qgroups which impact the given path(include ancestral
               qgroups)

           -f
               list all qgroups which impact the given path(exclude ancestral
               qgroups)

           --raw
               raw numbers in bytes, without the B suffix.

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

           --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.

           --kbytes
               show sizes in KiB, or kB with --si.

           --mbytes
               show sizes in MiB, or MB with --si.

           --gbytes
               show sizes in GiB, or GB with --si.

           --tbytes
               show sizes in TiB, or TB with --si.

           --sort=[+/-]<attr>[,[+/-]<attr>]...
               list qgroups in order of <attr>.

               <attr> can be one or more of
               qgroupid,rfer,excl,max_rfer,max_excl.

               Prefix '+' means ascending order and '-' means descending order
               of <attr>. If no prefix is given, use ascending order by
               default.

               If multiple <attr>s is given, use comma to separate.

           --sync
               To retrieve information after updating the state of qgroups,
               force sync of the filesystem identified by <path> before
               getting information.

QUOTA RESCAN
       The rescan reads all extent sharing metadata and updates the respective
       qgoups accordingly.

       The information consists of bytes owned exclusively (excl) or
       shared/referred to (rfer). There's no explicit information about which
       extents are shared or owned exclusively. This means when qgroup
       relationship changes, extent owners change and qgroup numbers are no
       longer consistent unless we do a full rescan.

       However there are cases where we can avoid a full rescan, if a
       subvolume whose rfer number equals its excl number, which means all
       bytes are exclusively owned, then assigning/removing this subvolume
       only needs to add/subtract rfer number from its parent qgroup. This can
       speed up the rescan.

EXIT STATUS
       btrfs qgroup 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-subvolume(8), btrfs-quota(8),

Btrfs v5.7                        07/02/2020                   BTRFS-QGROUP(8)

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