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

144 Using capabilities, templates and rules
Rules
also required to provide the Reliable capability, the inherits keyword
should be used as shown here:
volume_template MyReliableSnapshot {
inherits Reliable
provides Snapshot
rules {
...
}
};
This template provides the Snapshot capability through its own rules, and
also provides the Reliable capability by using rules from other templates.
Note: By allowing ISP to choose any template that provides the required
capability, the
requires keyword gives ISP more flexibility when allocating
storage. This behavior is known as dynamic inheritance.
When choosing a template with a required capability, ISP gives preference to
templates that provide only that capability. This behavior avoids giving
unrelated capabilities to a volume.
When searching for a template with a required capability, ISP chooses only
those templates that inherit or provide that capability.
When searching for a template with a required capability, ISP recursively
chooses templates that provide all the required capabilities.
Rules
Rules specify the criteria for allocating storage, the criteria for laying out VxVM
objects on storage, and the relationship between these objects. Rules can be
classified as storage selection rules that define how to choose storage, or as
storage layout rules that define how storage is to be used.
You can optionally precede any rule with the keyword
desired. This modifier
means that ISP tries to honor this rule, but it can discard it if the rule would
cause the allocation to fail. An optional integer after the
desired keyword
specifies the preference order value for the rule. If specified, this number must
be greater than or equal to 1. If no preference order value is specified for a rule,
a value of 1 is assumed. Rules with low preference order values are preferred to
be retained over rules with higher values. Rules with the same preference order
are discarded together.
In the following example, the
stripe rule can be dropped if there is insufficient
storage to fulfill the storage allocation request: