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

           The same as assign subcommand.

       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 v4.20.1                            01/23/2019                          BTRFS-QGROUP(8)

usage: btrfs qgroup <command> [options] <path>

    btrfs qgroup assign [options] <src> <dst> <path>
        Assign SRC as the child qgroup of DST
    btrfs qgroup remove <src> <dst> <path>
        Remove a child qgroup SRC from DST.
    btrfs qgroup create <qgroupid> <path>
        Create a subvolume quota group.
    btrfs qgroup destroy <qgroupid> <path>
        Destroy a quota group.
    btrfs qgroup show [options] <path>
        Show subvolume quota groups.
    btrfs qgroup limit [options] <size>|none [<qgroupid>] <path>
        Set the limits a subvolume quota group.

manage quota groups