3.10.2. Tune GFS atime Quantum

3.10.2. Tune GFS atime Quantum

When atime updates are enabled, GFS (by default) only updates them once an hour. The time quantum is a tunable parameter that can be adjusted using the gfs_tool command.

Each GFS node updates the access time based on the difference between its system time and the time recorded in the inode. It is required that system clocks of all GFS nodes in a cluster be synchronized. If a node's system time is out of synchronization by a significant fraction of the tunable parameter, atime_quantum, then atime updates are written more frequently. Increasing the frequency of atime updates may cause performance degradation in clusters with heavy work loads.

To see the current values of the GFS tunable parameters, including atime_quantum, you can use the gfs_tool gettune, as described in Section 3.4, “Displaying GFS Tunable Parameters”. The default value for atime_quantum is 3600 seconds.

The gfs_tool settune command is used to change the atime_quantum parameter value. It must be set on each node and each time the file system is mounted. The setting is not persistent across unmounts.

Usage

Changing the atime_quantum Parameter Value

gfs_tool settune MountPoint atime_quantum Seconds
MountPoint

Specifies the directory where the GFS file system is mounted.

Seconds

Specifies the update period in seconds.

Example

In this example, the atime update period is set to once a day (86,400 seconds) for the GFS file system on mount point /gfs.

gfs_tool settune /gfs atime_quantum 86400

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