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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Summary of Contents for GLOBAL FILE SYSTEM 5.2
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