236 lines
7.5 KiB
ReStructuredText
236 lines
7.5 KiB
ReStructuredText
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btrfs-qgroup(8)
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===============
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SYNOPSIS
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--------
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**btrfs qgroup** <subcommand> <args>
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DESCRIPTION
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-----------
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**btrfs qgroup** is used to control quota group (qgroup) of a btrfs filesystem.
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.. note::
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To use qgroup you need to enable quota first using **btrfs quota enable**
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command.
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.. warning::
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Qgroup is not stable yet and will impact performance in current mainline
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kernel (v4.14).
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QGROUP
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------
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Quota groups or qgroup in btrfs make a tree hierarchy, the leaf qgroups are
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attached to subvolumes. The size limits are set per qgroup and apply when any
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limit is reached in tree that contains a given subvolume.
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The limits are separated between shared and exclusive and reflect the extent
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ownership. For example a fresh snapshot shares almost all the blocks with the
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original subvolume, new writes to either subvolume will raise towards the
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exclusive limit.
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The qgroup identifiers conform to *level/id* where level 0 is reserved to the
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qgroups associated with subvolumes. Such qgroups are created automatically.
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The qgroup hierarchy is built by commands **create** and **assign**.
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.. note::
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If the qgroup of a subvolume is destroyed, quota about the subvolume will
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not be functional until qgroup *0/<subvolume id>* is created again.
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SUBCOMMAND
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----------
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assign [options] <src> <dst> <path>
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Assign qgroup *src* as the child qgroup of *dst* in the btrfs filesystem
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identified by *path*.
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``Options``
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--rescan
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(default since: 4.19) Automatically schedule quota rescan if the new qgroup
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assignment would lead to quota inconsistency. See *QUOTA RESCAN* for more
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information.
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--no-rescan
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Explicitly ask not to do a rescan, even if the assignment will make the quotas
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inconsistent. This may be useful for repeated calls where the rescan would add
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unnecessary overhead.
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create <qgroupid> <path>
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Create a subvolume quota group.
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For the *0/<subvolume id>* qgroup, a qgroup can be created even before the
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subvolume is created.
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destroy <qgroupid> <path>
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Destroy a qgroup.
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If a qgroup is not isolated, meaning it is a parent or child qgroup, then it
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can only be destroyed after the relationship is removed.
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limit [options] <size>|none [<qgroupid>] <path>
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Limit the size of a qgroup to *size* or no limit in the btrfs filesystem
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identified by *path*.
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If *qgroupid* is not given, qgroup of the subvolume identified by *path*
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is used if possible.
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``Options``
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-c
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limit amount of data after compression. This is the default, it is currently not
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possible to turn off this option.
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-e
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limit space exclusively assigned to this qgroup.
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remove <src> <dst> <path>
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Remove the relationship between child qgroup *src* and parent qgroup *dst* in
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the btrfs filesystem identified by *path*.
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``Options``
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--rescan
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(default since: 4.19) Automatically schedule quota rescan if the removed qgroup
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relation would lead to quota inconsistency. See *QUOTA RESCAN* for more
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information.
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--no-rescan
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Explicitly ask not to do a rescan, even if the removal will make the quotas
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inconsistent. This may be useful for repeated calls where the rescan would add
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unnecessary overhead.
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show [options] <path>
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Show all qgroups in the btrfs filesystem identified by <path>.
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``Options``
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-p
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print parent qgroup id.
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-c
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print child qgroup id.
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-r
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print limit of referenced size of qgroup.
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-e
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print limit of exclusive size of qgroup.
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-F
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list all qgroups which impact the given path(include ancestral qgroups)
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-f
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list all qgroups which impact the given path(exclude ancestral qgroups)
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--raw
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raw numbers in bytes, without the *B* suffix.
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--human-readable
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print human friendly numbers, base 1024, this is the default
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--iec
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select the 1024 base for the following options, according to the IEC standard.
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--si
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select the 1000 base for the following options, according to the SI standard.
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--kbytes
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show sizes in KiB, or kB with --si.
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--mbytes
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show sizes in MiB, or MB with --si.
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--gbytes
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show sizes in GiB, or GB with --si.
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--tbytes
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show sizes in TiB, or TB with --si.
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--sort=[\+/-]<attr>[,[+/-]<attr>]...
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list qgroups in order of <attr>.
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<attr> can be one or more of qgroupid,rfer,excl,max_rfer,max_excl.
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Prefix *+* means ascending order and *-* means descending order of *attr*.
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If no prefix is given, use ascending order by default.
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If multiple *attr* values are given, use comma to separate.
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--sync
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To retrieve information after updating the state of qgroups,
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force sync of the filesystem identified by *path* before getting information.
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QUOTA RESCAN
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------------
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The rescan reads all extent sharing metadata and updates the respective qgoups
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accordingly.
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The information consists of bytes owned exclusively (*excl*) or shared/referred
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to (*rfer*). There's no explicit information about which extents are shared or
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owned exclusively. This means when qgroup relationship changes, extent owners
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change and qgroup numbers are no longer consistent unless we do a full rescan.
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However there are cases where we can avoid a full rescan, if a subvolume whose
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*rfer* number equals its *excl* number, which means all bytes are exclusively
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owned, then assigning/removing this subvolume only needs to add/subtract *rfer*
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number from its parent qgroup. This can speed up the rescan.
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EXAMPLES
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--------
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Make a parent group that has two quota group children
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Given the following filesystem mounted at `/mnt/my-vault`
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.. code-block:: none
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Label: none uuid: 60d2ab3b-941a-4f22-8d1a-315f329797b2
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Total devices 1 FS bytes used 128.00KiB
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devid 1 size 5.00GiB used 536.00MiB path /dev/vdb
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Enable quota and create subvolumes. Check subvolume ids.
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.. code-block:: bash
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$ cd /mnt/my-vault
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$ btrfs quota enable .
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$ btrfs subvolume create a
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$ btrfs subvolume create b
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$ btrfs subvolume list .
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ID 261 gen 61 top level 5 path a
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ID 262 gen 62 top level 5 path b
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Create qgroup and set limit to 10MiB.
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.. code-block:: bash
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$ btrfs qgroup create 1/100 .
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$ btrfs qgroup limit 10M 1/100 .
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$ btrfs qgroup assign 0/261 1/100 .
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$ btrfs qgroup assign 0/262 1/100 .
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And check qgroups.
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.. code-block:: bash
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$ btrfs qgroup show .
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qgroupid rfer excl
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-------- ---- ----
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0/5 16.00KiB 16.00KiB
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0/261 16.00KiB 16.00KiB
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0/262 16.00KiB 16.00KiB
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1/100 32.00KiB 32.00KiB
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EXIT STATUS
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-----------
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**btrfs qgroup** returns a zero exit status if it succeeds. Non zero is
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returned in case of failure.
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AVAILABILITY
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------------
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**btrfs** is part of btrfs-progs.
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Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for
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further details.
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SEE ALSO
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--------
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``mkfs.btrfs(8)``,
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``btrfs-subvolume(8)``,
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``btrfs-quota(8)``,
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