Storage Layout Rules

The following sections describe storage layout rules:

• apply
• parity
• striped

See Compound Rules for details of how to limit the scope of interpretation of rules to the components of an application volume, such as its plexes, columns and logs.

apply

The apply rule is used to apply rules from one or more specified templates in addition to the rules that appear in the current template. This rule acts recursively if the specified templates also use apply in their rules sections. The capabilities of any referenced templates are not used.

Expressions involving apply can specify the eachof or oneof operator. The default operator for this keyword is eachof.

The following examples demonstrate the application of the apply rule:

• Apply the rules but not the capabilities from the template ArrayProductId to a compound rule within the template PrefabricatedDataMirroring:

volume_template PrefabricatedDataMirroring {
  provides PrefabricatedDataMirroring
  rules {
   apply ArrayProductId
   confineto eachof ( "Redundancy" =nmirs , "Parity" ="0"  )
  }
};

volume_template ArrayProductId {
  provides ArrayProductId
  rules {
   confineto "ProductId"
  }
};
• Typically, you would use the apply keyword when you want to get the rules of a template without its associated capabilities. In the example, the template MyReliableSnapshot is defined so that the application of Snapshot to one mirror results in the whole volume getting the associated Snapshot capability, whereas the application of EMCStorage to one mirror does not result in the whole volume getting the EMCStorage capability:

volume_template MyReliableSnapshot {
  provides Snapshot, Reliable
  rules {
   separateby "Enclosure"
   mirror 1 {
    apply Snapshot, EMCStorage
    confineto "Enclosure"
   }
   mirror 1 {
    confineto "Enclosure"
   }
  }
};

parity

The parity rule defines whether redundancy should be parity based (that is, RAID-5) as implemented in either hardware or software. The value can be true or false.

The following example demonstrates the application of the parity rule:

• Define a template for providing reliability using software RAID-5:

volume_template Raid5Volume {
  provides Raid5Capability, Raid5LogMirroring
  rules {
   parity true
   stripe ncols - nmaxcols
   log nlogs {
    type raid5
   }
  }
};

striped

The striped rule indicates whether a volume or mirror is to be striped.

If striped is set to true, the number of columns is not necessarily greater than one as striping can be implemented in hardware as well as software.

The following example demonstrates the application of the striped rule:

• Define a template for providing reliability using mirrors, but where striping is not allowed:

volume_template ReliableConcat {
  provides Reliable, Concat
  rules {
   mirror NMIRS
   striped false
  }
};