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|
btrfs-qgroup(8)
===============
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`
.. code-block:: none
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.
.. code-block:: bash
$ 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.
.. code-block:: bash
$ 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.
.. code-block:: bash
$ 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 or wiki http://btrfs.wiki.kernel.org for further
information.
SEE ALSO
--------
:doc:`btrfs-quota(8)<btrfs-quota>`,
:doc:`btrfs-subvolume(8)<btrfs-subvolume>`,
:doc:`mkfs.btrfs(8)<mkfs.btrfs>`,
|
