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

100 Administering instant snapshots
Creating a shared cache volume and preparing space-optimized snapshots
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 increase the size of the cache
manually, or use the
vxcache set command to reduce the value of
highwatermark for the cache object, as shown in this example:
# vxcache -g mydg set highwatermark=60 cobjmydg
See “Growing and shrinking a cache” on page 100.
You can use the maxautogrow attribute to limit the maximum size to which a
cache can grow. To estimate this size, consider how much the contents of each
source volume are likely to change between snapshot refreshes, and allow some
additional space for contingency.
If necessary, you can use the
vxcache set command to change other autogrow
attribute values for a cache. See the
vxcache(1M) manual page for details.
Note: Ensure that the cache is sufficiently large, and that the autogrow
attributes are configured correctly for your needs.
Growing and shrinking a cache
You can use the vxcache command to increase the size of the cache volume that
is associated with a cache object:
# vxcache [-g diskgroup ] growcacheto cache_object size
For example, to increase the size of the cache volume associated with the cache,
mycache, to 2GB, use the following command:
# vxcache -g mydg growcacheto mycache 2g
To grow a cache by a specified amount, use the following form of the command:
# vxcache [-g diskgroup ] growcacheby cache_object size
For example, to increase the size of the cache, mycache, by 1GB, you would use
the following command:
# vxcache -g mydg growcacheby mycache 1g
You can similarly use the shrinkcacheby and shrinkcacheto operations to
reduce the size of a cache. See the
vxcache(1M) manual page for more
information.