Designing Disaster Recovery Clusters using Metroclusters and Continentalclusters, Reprinted October 2011 (5900-1881)

When creating disk groups and distributing Vdisks within them, sufficient capacity must remain
for log disks to expand to their maximum level. The log is declared full, and reaches its maximum
level, whenever the first of the following conditions is reached:
• The size of the log data file exceeds twice the capacity of the DR group.
• No free space remains in the physical disk group.
• The log reaches 2 TB of Vraid1 (4 TB total).
Copy Sets
Vdisks are user-defined storage allotments of virtual or logical data storage. A pairing relationship
can be created to automatically replicate a logical disk to another logical disk. The generic term
for this is a copy set. A relationship refers to the arrangement created when two storage systems
are partnered for the purpose of replicating data between them. A Vdisk does not have to be part
of a copy set. Vdisks at any site can be set up for local storage and used for activities such as
testing and backup. Clones and snapclones are examples of Vdisks used in this manner. When a
Vdisk is not part of a copy set, it is not disaster tolerant, but it can use various Vraid types for
failure tolerance.
Managed Sets
A managed set is a collection of DR groups selected for the purpose of managing them. For
example, a managed set can be created to manage all DR groups of a particular application that
reside in separate storage arrays.
Failover
The recovery process whereby one DR group, managed set, fabric, or controller switches over to
its backup is called a failover. The process can be planned or unplanned. A planned failover
allows an orderly shutdown of the system before the redundant system takes over. An unplanned
failover occurs when a failure or outage occurs that may not allow an orderly transition of roles.
Listed below are several types of Continuous Access EVA failovers:
• DR group failover: An operation to reverse the replication direction of a DR group. A DR group
can have a relationship with only one other DR group, and a storage system can have a
relationship with only one other storage system.
• Managed set failover: An operation to reverse the replication direction of all DR groups in
the managed set.
• Fabric or path failover: The act of transferring I/O operations from one fabric or path to
another.
• Controller failover: When a controller assumes the workload of its partner (within the same
storage system).
Continuous Access EVA Management Software
Metrocluster Continuous Access EVA requires the following two software components to be installed
in the Management Server:
• HP StorageWorks Command View EVA (CV EVA). This software component allows you to
configure and manage the storage and DR group via a web browser interface.
• Storage Management Interface Specification (SMI-S). The SMI-S EVA software provides the
Storage Management Interface Specification (SMI-S) interface for the management of EVA
arrays. Metrocluster Continuous Access EVA software uses WBEM API to communicate with
SMI-S to automatically manage the DR Groups that are used in the application packages.
Overview of EVA and Continuous Access EVA Concepts 215