btrfs-qgroup(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | QGROUP | SUBCOMMAND | QUOTA RESCAN | EXAMPLES | EXIT STATUS | AVAILABILITY | SEE ALSO | COLOPHON

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

NAME         top

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

SYNOPSIS         top

       btrfs qgroup <subcommand> <args>

DESCRIPTION         top

       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         top

       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         top

       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         top

       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.

EXAMPLES         top

       Example 1. 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         top

       btrfs qgroup returns a zero exit status if it succeeds. Non zero
       is returned in case of failure.

AVAILABILITY         top

       btrfs is part of btrfs-progs. Please refer to the btrfs wiki
       http://btrfs.wiki.kernel.org for further details.

SEE ALSO         top

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

COLOPHON         top

       This page is part of the btrfs-progs (btrfs filesystem tools)
       project.  Information about the project can be found at 
       ⟨https://btrfs.wiki.kernel.org/index.php/Btrfs_source_repositories⟩.
       If you have a bug report for this manual page, see
       ⟨https://btrfs.wiki.kernel.org/index.php/Problem_FAQ#How_do_I_report_bugs_and_issues.3F⟩.
       This page was obtained from the project's upstream Git repository
       ⟨git://git.kernel.org/pub/scm/linux/kernel/git/kdave/btrfs-progs.git⟩
       on 2021-06-20.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-05-13.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

Btrfs v4.6.1                   10/25/2020                BTRFS-QGROUP(8)

Pages that refer to this page: tmpfiles.d(5)btrfs(8)btrfs-quota(8)btrfs-subvolume(8)