4.9.2. 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.
By using the gettune flag of the gfs_tool command, all current tunable parameters including atime_quantum (default is 3600 seconds) are displayed.
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.)
Displaying Tunable Parameters
gfs_tool gettune MountPoint
-
MountPoint
-
Specifies the directory where the GFS file system is mounted.
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.
In this example, all GFS tunable parameters for the file system on the mount point /gfs1 are displayed.
gfs_tool gettune /gfs1
In this example, the atime update period is set to once a day (86,400 seconds) for the GFS file system on mount point /gfs1.
gfs_tool settune /gfs1 atime_quantum 86400
