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btrfs-progs: doc: update qgroup docs

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Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2015-07-27 17:36:03 +02:00
parent e5a6610c94
commit c78f3eea94
2 changed files with 18 additions and 14 deletions
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24
Documentation/btrfs-qgroup.asciidoc
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@ -11,25 +11,29 @@ SYNOPSIS
DESCRIPTION
-----------
*btrfs qgroup* is used to control quota group(qgroup) of a btrfs filesystem.
*btrfs qgroup* is used to control quota group (qgroup) of a btrfs filesystem.
NOTE: To use qgroup, it needs to enable quota first using *btrfs quota*
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(v3.14 so far).
kernel (v3.14 so far).
QGROUP
------
Quota group or qgroup in btrfs has its hierarchy like subvolume.
One subvolume/snapshot can reach its quota limits if it consumes all the quota
assigned to it or any of the parent qgroup(s).
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.
Also for snapshot, it consumes no quota initially since all its data
shares with its parent, so only modification in snapshot consumes quota.
The limit sare 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.
Every subvolume/snapshot will have its own qgroup with id '0/<subvolume id>'
upon creating, but can be later destroyed by *btrfs qgroup destroy* command.
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.

8
cmds-qgroup.c
View File

@ -206,7 +206,7 @@ static int parse_limit(const char *p, unsigned long long *s)
static const char * const cmd_qgroup_assign_usage[] = {
"btrfs qgroup assign [options] <src> <dst> <path>",
"Enable subvolume qgroup support for a filesystem.",
"Assign SRC as the child qgroup of DST",
"",
"--rescan schedule qutoa rescan if needed",
"--no-rescan ",
@ -223,7 +223,7 @@ static int cmd_qgroup_assign(int argc, char **argv)
static const char * const cmd_qgroup_remove_usage[] = {
"btrfs qgroup remove <src> <dst> <path>",
"Remove a subvol from a quota group.",
"Remove a child qgroup SRC from DST.",
NULL
};
@ -251,7 +251,7 @@ static int cmd_qgroup_create(int argc, char **argv)
static const char * const cmd_qgroup_destroy_usage[] = {
"btrfs qgroup destroy <qgroupid> <path>",
"Destroy a subvolume quota group.",
"Destroy a quota group.",
NULL
};
@ -419,7 +419,7 @@ static int cmd_qgroup_show(int argc, char **argv)
static const char * const cmd_qgroup_limit_usage[] = {
"btrfs qgroup limit [options] <size>|none [<qgroupid>] <path>",
"Limit the size of a subvolume quota group.",
"Set the limits a subvolume quota group.",
"",
"-c limit amount of data after compression. This is the default,",
" it is currently not possible to turn off this option.",