Mount With Noatime; Tune Gfs Atime Quantum - Red Hat ENTERPRISE LINUX 4 - GLOBAL FILE SYTEM Manual

Chapter 4. Managing GFS
• 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
If 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 atime updates.
Two methods of reducing the effects of atime updating are available:

• Mount with noatime

• Tune GFS atime quantum

4.9.1. Mount with noatime
A standard Linux mount option, noatime, can be specified when the file system is mounted, which
disables atime updates on that file system.
Usage
mount -t gfs BlockDevice MountPoint -o noatime
BlockDevice
Specifies the block device where the GFS file system resides.
MountPoint
Specifies the directory where the GFS file system should be mounted.
Example
In this example, the GFS file system resides on the /dev/vg01/lvol0 and is mounted on directory /
gfs1 with atime updates turned off.
mount -t gfs /dev/vg01/lvol0 /gfs1 -o noatime
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.
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