HP P6000 Cluster Extension Software Administrator Guide (5697-0986, June 2011)

Disaster tolerance through geographical dispersion
Using two or more storage systems, HP P6000 Continuous Access copies data to a remote data
center. Cluster solutions using P6000 Continuous Access disk mirroring are called metropolitan clusters
or geographically dispersed clusters. In this arrangement, a server is a member of the same cluster
dispersed over two or more sites. In such clusters the server is relieved from writing any I/O request
to the disk more than one time because the storage system controls the replication process (see Figure
1 on page 10).
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.
P6000 Cluster Extension features10