HP P6000 Cluster Extension Software Administrator Guide (5697-2274, November 2012)

Figure 1 Physical replication using HP P6000 Continuous Access
P6000 Continuous Access-mirrored disks have a read/write-enabled source (local) disk and a
read-only destination (remote) disk. Current cluster software products cannot distinguish between
read-only and write-enabled disks, and cannot enable disk access if the disk is not write-enabled
during the server boot process.
With P6000 Cluster Extension, the consistency and concurrency of the data can be checked when
the resource comes online in the remote data center. The capability for restoring the application
service after a failure of the server is called disaster tolerance.
Automated redirection of mirrored disks
Storage systems with P6000 Continuous Access automatically redirect the mirroring destination.
This means that P6000 Continuous Access almost instantaneously swaps the source/destination
relationship of DR group members if the application must access the destination disk (vdisk). This
feature ensures that the disks are always accessible when failover to a remote data center occurs.
NOTE: Vdisks are virtual disks used in a HP P6000/EVA storage system for the storage of
application data. A DR group includes one or more vdisks in a P6000/EVA storage system. The
DR group is the unit in which P6000 Cluster Extension failover/failback operations are performed.
For more information about DR groups, see the HP P6000 Continuous Access Implementation
Guide.
If the links between your storage systems are broken, depending on the configuration, the source
P6000/EVA array can log all the write I/Os of a DR group member to a write history log and
replicate the changes later after the links become available. In case of a failover, P6000 Cluster
Extension takes the appropriate action for each link/array status and makes sure that your
application service has the latest data.
Cluster setup considerations
For quorum considerations that apply to Windows, see “MSCS” (page 8).
Automated redirection of mirrored disks 7