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NAME | SYNOPSIS | DESCRIPTION | QGROUP | SUBCOMMAND | QUOTA RESCAN | EXAMPLES | EXIT STATUS | AVAILABILITY | SEE ALSO | COLOPHON |
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BTRFS-QGROUP(8) Btrfs Manual BTRFS-QGROUP(8)
btrfs-qgroup - control the quota group of a btrfs filesystem
btrfs qgroup <subcommand> <args>
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).
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.
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.
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.
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
btrfs qgroup returns a zero exit status if it succeeds. Non zero
is returned in case of failure.
btrfs is part of btrfs-progs. Please refer to the btrfs wiki
http://btrfs.wiki.kernel.org for further details.
mkfs.btrfs(8), btrfs-subvolume(8), btrfs-quota(8),
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 2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-05-02.) 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 [email protected]
Btrfs v5.16.1 02/06/2022 BTRFS-QGROUP(8)
Pages that refer to this page: tmpfiles.d(5), btrfs(8), btrfs-quota(8), btrfs-subvolume(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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