A storage policy can include one or several rule sets that describe requirements for virtual machine storage resources. It can also include common rules.
If common rules are not available in your environment or not defined, you can create a policy that includes datastore-specific rule sets. To define a policy, one rule set is required. Additional rule sets are optional. Multiple rule sets allow a single policy to define alternative selection parameters, often from several storage providers.
A single rule set contains one or several rules. Each rule can be based on a single underlying data service that a storage entity guarantees. The rule describes a specific quality or quantity that the storage resource must provide. You can also reference user-defined datastore tags in the rules. One datastore-specific rule set can include rules from only a single storage entity.
The relationship between all rule sets within a policy is defined by the Boolean operator OR, whereas the relationship between all rules within a single rule set is defined by AND. Meeting all the rules of any one rule set is sufficient to satisfy the entire policy. Each rule set represents an equally acceptable set of constraints.
If common rules are enabled, the policy is required to include either common rules or at least one datastore-specific rule set. If you define both common rules and datastore-specific rules, the storage policy matches datastores that satisfy all common rules and all rules in at least one of the rule sets.