Veritas Storage Foundation Intelligent Storage Provisioning 5.0 AdministratorÆs Guide, HP-UX 11i v3, First Edition, May 2008

99Administering instant snapshots
Creating a shared cache volume and preparing space-optimized snapshots
.
.
};
!!
Note: Because of its complexity, it is recommended that you run this command
as a script.
For the examples given earlier in this section, the combined form of the
command would be:
# vxassist -M make <<!!
volumegroup {
diskgroup "mydg"
volume "mycache" 1g {
type cachevolume
capability ’DataMirroring(nmirs=2)’
}
volume "mysovol" 10g {
init active
cachevolume "
cachevol "
}
};
!!
Tuning the autogrow attributes
The highwatermark, autogrowby and maxautogrow attributes determine
how the VxVM cache daemon (
vxcached) maintains the cache if the autogrow
feature has been enabled and
vxcached is running:
■ When cache usage reaches the high watermark value, highwatermark
(default value is 90 percent),
vxcached grows the size of the cache volume by
the value of autogrowby (default value is 20% of the size of the cache
volume in blocks). The new required cache size cannot exceed the value of
maxautogrow (default value is twice the size of the cache volume in blocks).
■ When cache usage reaches the high watermark value, and the new required
cache size would exceed the value of maxautogrow,
vxcached deletes the
oldest snapshot in the cache. If there are several snapshots with the same
age, the largest of these is deleted.
If the autogrow feature has been disabled:
■ When cache usage reaches the high watermark value, vxcached deletes the
oldest snapshot in the cache. If there are several snapshots with the same
age, the largest of these is deleted. If there is only a single snapshot, this
snapshot is detached and marked as invalid.