Each file inode and directory inode has three time stamps associated with it:
ctime — The last time the inode status was changed
mtime — The last time the file (or directory) data was modified
atime — The last time the file (or directory) data was accessed
atime updates are enabled as they are by default on GFS and other Linux file systems then every time a file is read, its inode needs to be updated.
Because few applications use the information provided by
atime, those updates can require a significant amount of unnecessary write traffic and file-locking traffic. That traffic can degrade performance; therefore, it may be preferable to turn off
Two methods of reducing the effects of
atime updating are available:
4.11.1. Mount with
A standard Linux mount option,
noatime, can be specified when the file system is mounted, which disables
atime updates on that file system.
BlockDevice MountPoint -o noatime
Specifies the block device where the GFS file system resides.
Specifies the directory where the GFS file system should be mounted.
In this example, the GFS file system resides on the
/dev/vg01/lvol0 and is mounted on directory
/gfs with atime updates turned off.
mount /dev/vg01/lvol0 /gfs -o noatime
4.11.2. Tune GFS
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
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 updates are written more frequently. Increasing the frequency of
atime updates may cause performance degradation in clusters with heavy work loads.
gfs_tool 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.
atime_quantum Parameter Value
Specifies the directory where the GFS file system is mounted.
Specifies the update period in seconds.
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_tool settune /gfs atime_quantum 86400