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4179885cf9
This patch adds examples section in btrfs-qgroup documentation. The example make a quota group that has two subvolumes as children. Signed-off-by: Sidong Yang <realwakka@gmail.com> Signed-off-by: David Sterba <dsterba@suse.com>
234 lines
6.6 KiB
Plaintext
234 lines
6.6 KiB
Plaintext
btrfs-qgroup(8)
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===============
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NAME
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----
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btrfs-qgroup - control the quota group of a btrfs filesystem
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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: To use qgroup you need to enable quota first using *btrfs quota enable*
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command.
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WARNING: 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: If the qgroup of a subvolume is destroyed, quota about the subvolume
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will 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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+
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`Options`
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+
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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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+
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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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+
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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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+
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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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+
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`Options`
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+
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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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+
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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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+
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`Options`
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+
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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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+
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`Options`
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+
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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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+
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<attr> can be one or more of qgroupid,rfer,excl,max_rfer,max_excl.
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+
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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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+
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If multiple <attr>s is given, use comma to separate.
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+
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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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----
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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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----
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Enable quota and create subvolumes. Check subvolume ids.
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[source,bash]
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----
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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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----
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Create qgroup and set limit to 10MiB.
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[source,bash]
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----
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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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----
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And check qgroups.
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[source,bash]
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----
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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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----
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====
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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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