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3.4. GFS2 Quota Management
File system quotas are used to limit the amount of file system space a user or group can use. A user or group does not have a quota limit until one is set. When a GFS2 file system is mounted with the
quota=on or quota=account option, GFS2 keeps track of the space used by each user and group even when there are no limits in place. GFS2 updates quota information in a transactional way so system crashes do not require quota usages to be reconstructed.
To prevent a performance slowdown, a GFS2 node synchronizes updates to the quota file only periodically. The fuzzy quota accounting can allow users or groups to slightly exceed the set limit. To minimize this, GFS2 dynamically reduces the synchronization period as a hard quota limit is approached.
Note
GFS2 supports the standard Linux quota facilities. In order to use this you will need to install the quota RPM. This is the preferred way to administer quotas on GFS2 and should be used for all new deployments of GFS2 using quotas. This section documents GFS2 quota management using these facilities.
3.4.1. Configuring Disk Quotas
To implement disk quotas, use the following steps:
- Set up quotas in enforcement or accounting mode.
- Initialize the quota database file with current block usage information.
- Assign quota policies. (In accounting mode, these policies are not enforced.)
Each of these steps is discussed in detail in the following sections.
3.4.1.1. Setting Up Quotas in Enforcement or Accounting Mode
In GFS2 file systems, quotas are disabled by default. To enable quotas for a file system, mount the file system with the
quota=on option specified.
It is possible to keep track of disk usage and maintain quota accounting for every user and group without enforcing the limit and warn values. To do this, mount the file system with the
quota=account option specified.
To mount a file system with quotas enabled, specify
quota=on for the options argument when creating the GFS2 file system resource in a cluster. For example, the following command specifies that the GFS2 Filesystem resource being created will be mounted with quotas enabled.
# pcs resource create gfs2mount Filesystem options="quota=on" device=BLOCKDEVICE directory=MOUNTPOINT fstype=gfs2 clone
For information on configuring a GFS2 file system in a Pacemaker cluster, see Chapter 5, Configuring a GFS2 File System in a Cluster.
To mount a file system with quota accounting maintained, even though the quota limits are not enforced, specify
quota=account for the options argument when creating the GFS2 file system resource in a cluster.
To mount a file system with quotas disabled, specify
quota=off for the options argument when creating the GFS2 file system resource in a cluster.
3.4.1.2. Creating the Quota Database Files
After each quota-enabled file system is mounted, the system is capable of working with disk quotas. However, the file system itself is not yet ready to support quotas. The next step is to run the
quotacheck command.
The
quotacheck command examines quota-enabled file systems and builds a table of the current disk usage per file system. The table is then used to update the operating system's copy of disk usage. In addition, the file system's disk quota files are updated.
To create the quota files on the file system, use the
-u and the -g options of the quotacheck command; both of these options must be specified for user and group quotas to be initialized. For example, if quotas are enabled for the /home file system, create the files in the /home directory:
quotacheck -ug /home
3.4.1.3. Assigning Quotas Per User
The last step is assigning the disk quotas with the
edquota command. Note that if you have mounted your file system in accounting mode (with the quota=account option specified), the quotas are not enforced.
To configure the quota for a user, as root in a shell prompt, execute the command:
# edquota username
Perform this step for each user who needs a quota. For example, if a quota is enabled for the
/home partition (/dev/VolGroup00/LogVol02 in the example below) and the command edquota testuser is executed, the following is shown in the editor configured as the default for the system:
Disk quotas for user testuser (uid 501): Filesystem blocks soft hard inodes soft hard /dev/VolGroup00/LogVol02 440436 0 0
Note
The text editor defined by the
EDITOR environment variable is used by edquota. To change the editor, set the EDITOR environment variable in your ~/.bash_profile file to the full path of the editor of your choice.
The first column is the name of the file system that has a quota enabled for it. The second column shows how many blocks the user is currently using. The next two columns are used to set soft and hard block limits for the user on the file system.
The soft block limit defines the maximum amount of disk space that can be used.
The hard block limit is the absolute maximum amount of disk space that a user or group can use. Once this limit is reached, no further disk space can be used.
The GFS2 file system does not maintain quotas for inodes, so these columns do not apply to GFS2 file systems and will be blank.
If any of the values are set to 0, that limit is not set. In the text editor, change the limits. For example:
Disk quotas for user testuser (uid 501): Filesystem blocks soft hard inodes soft hard /dev/VolGroup00/LogVol02 440436 500000 550000
To verify that the quota for the user has been set, use the command:
quota testuser
3.4.1.4. Assigning Quotas Per Group
Quotas can also be assigned on a per-group basis. Note that if you have mounted your file system in accounting mode (with the
account=on option specified), the quotas are not enforced.
To set a group quota for the
devel group (the group must exist prior to setting the group quota), use the following command:
edquota -g devel
This command displays the existing quota for the group in the text editor:
Disk quotas for group devel (gid 505): Filesystem blocks soft hard inodes soft hard /dev/VolGroup00/LogVol02 440400 0 0
The GFS2 file system does not maintain quotas for inodes, so these columns do not apply to GFS2 file systems and will be blank. Modify the limits, then save the file.
To verify that the group quota has been set, use the following command:
$ quota -g devel3.4.2. Managing Disk Quotas
If quotas are implemented, they need some maintenance — mostly in the form of watching to see if the quotas are exceeded and making sure the quotas are accurate.
Of course, if users repeatedly exceed their quotas or consistently reach their soft limits, a system administrator has a few choices to make depending on what type of users they are and how much disk space impacts their work. The administrator can either help the user determine how to use less disk space or increase the user's disk quota.
You can create a disk usage report by running the
repquota utility. For example, the command repquota /home produces this output:
*** Report for user quotas on device /dev/mapper/VolGroup00-LogVol02 Block grace time: 7days; Inode grace time: 7days Block limits File limits User used soft hard grace used soft hard grace ---------------------------------------------------------------------- root -- 36 0 0 4 0 0 kristin -- 540 0 0 125 0 0 testuser -- 440400 500000 550000 37418 0 0
To view the disk usage report for all (option
-a) quota-enabled file systems, use the command:
# repquota -a
While the report is easy to read, a few points should be explained. The
-- displayed after each user is a quick way to determine whether the block limits have been exceeded. If the block soft limit is exceeded, a + appears in place of the first - in the output. The second - indicates the inode limit, but GFS2 file systems do not support inode limits so that character will remain as -. GFS2 file systems do not support a grace period, so the grace column will remain blank.
Note that the
repquota command is not supported over NFS, irrespective of the underlying file system.
3.4.3. Keeping Quotas Accurate
If you enable quotas on your file system after a period of time when you have been running with quotas disabled, you should run the
quotacheck command to create, check, and repair quota files. Additionally, you may want to run the quotacheck command if you think your quota files may not be accurate, as may occur when a file system is not unmounted cleanly after a system crash.
For more information about the
quotacheck command, see the quotacheck man page.
Note
Run
quotacheck when the file system is relatively idle on all nodes because disk activity may affect the computed quota values.
3.4.4. Synchronizing Quotas with the quotasync Command
GFS2 stores all quota information in its own internal file on disk. A GFS2 node does not update this quota file for every file system write; rather, by default it updates the quota file once every 60 seconds. This is necessary to avoid contention among nodes writing to the quota file, which would cause a slowdown in performance.
As a user or group approaches their quota limit, GFS2 dynamically reduces the time between its quota-file updates to prevent the limit from being exceeded. The normal time period between quota synchronizations is a tunable parameter,
quota_quantum. You can change this from its default value of 60 seconds using the quota_quantum= mount option, as described in Table 3.2, “GFS2-Specific Mount Options”. The quota_quantum parameter must be set on each node and each time the file system is mounted. Changes to the quota_quantum parameter are not persistent across unmounts. You can update the quota_quantum value with the mount -o remount.
You can use the
quotasync command to synchronize the quota information from a node to the on-disk quota file between the automatic updates performed by GFS2.
Usage
Synchronizing Quota Information
quotasync [-ug] -a|mntpnt...
u- Sync the user quota files.
g- Sync the group quota files
a- Sync all file systems that are currently quota-enabled and support sync. When -a is absent, a file system mountpoint should be specified.
mntpnt- Specifies the GFS2 file system to which the actions apply.
Tuning the Time Between Synchronizations
mount -o quota_quantum=secs,remount BlockDevice MountPointMountPoint- Specifies the GFS2 file system to which the actions apply.
secs- Specifies the new time period between regular quota-file synchronizations by GFS2. Smaller values may increase contention and slow down performance.
Examples
This example synchronizes all the cached dirty quotas from the node it is run on to the on-disk quota file for the file system
/mnt/mygfs2.
# quotasync -ug /mnt/mygfs2
This example changes the default time period between regular quota-file updates to one hour (3600 seconds) for file system
/mnt/mygfs2 when remounting that file system on logical volume /dev/volgroup/logical_volume.
# mount -o quota_quantum=3600,remount /dev/volgroup/logical_volume /mnt/mygfs2