Provided by: btrfs-progs_6.6.3-1.2_amd64 bug

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.

       clear-stale <path>
              Clear  all  stale  qgroups whose subvolume does not exist anymore, this is the level 0 qgroup like
              0/subvolid. Higher level qgroups are not deleted even if they don't have any child qgroups.

       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 values are 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 qgroups 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.

EXAMPLES

   Make a parent group that has two quota group children
       Given the following filesystem mounted at /mnt/my-vault

          Label: none  uuid: 60d2ab3b-941a-4f22-8d1a-315f329797b2
                 Total devices 1 FS bytes used 128.00KiB
                 devid    1 size 5.00GiB used 536.00MiB path /dev/vdb

       Enable quota and create subvolumes.  Check subvolume ids.

          $ cd /mnt/my-vault
          $ btrfs quota enable .
          $ btrfs subvolume create a
          $ btrfs subvolume create b
          $ btrfs subvolume list .

          ID 261 gen 61 top level 5 path a
          ID 262 gen 62 top level 5 path b

       Create qgroup and set limit to 10MiB.

          $ btrfs qgroup create 1/100 .
          $ btrfs qgroup limit 10M 1/100 .
          $ btrfs qgroup assign 0/261 1/100 .
          $ btrfs qgroup assign 0/262 1/100 .

       And check qgroups.

          $ btrfs qgroup show .

          qgroupid         rfer         excl
          --------         ----         ----
          0/5          16.00KiB     16.00KiB
          0/261        16.00KiB     16.00KiB
          0/262        16.00KiB     16.00KiB
          1/100        32.00KiB     32.00KiB

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 documentation at https://btrfs.readthedocs.io.

SEE ALSO

       btrfs-quota(8), btrfs-subvolume(8), mkfs.btrfs(8)