Provided by: btrfs-progs_6.3.2-1_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),