Red Hat GLOBAL FILE SYSTEM 5.2 Installationsanleitung PDF herunterladen (Seite 45)

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 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

11. Suspending Activity on a File System

You can suspend write activity to a file system by using the gfs_tool freeze command.

Suspending write activity allows hardware-based device snapshots to be used to capture the file

system in a consistent state. The gfs_tool unfreeze command ends the suspension.

Suspending Activity on a File System

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Red Hat GLOBAL FILE SYSTEM 5.2 Installationsanleitung Seite 45