Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Creating a Shared Cache Object
296 VERITAS Volume Manager Administrator’s Guide
Listing the Snapshots Created on a Cache
To list the space-optimized instant snapshots that have been created on a cache object, use
the following command:
# vxcache [-g diskgroup] listvol cache_object
The snapshot names are printed as a space-separated list ordered by timestamp. If two or
more snapshots have the same timestamp, these snapshots are sorted in order of
decreasing size.
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.
Note The vxcached daemon does not remove snapshots that are currently open, and it
does not remove the last or only snapshot in the cache.
If the cache space becomes exhausted, the snapshot is detached and marked as invalid. If
this happens, the snapshot is unrecoverable and must be removed. Enabling the
autogrow feature on the cache helps to avoid this situation occurring. However, for very
small caches (of the order of a few megabytes), it is possible for the cache to become
exhausted before the system has time to respond and grow the cache. In such cases, either