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),