HP XP Cluster Extension Software Administrator Guide

HP recommends a minimum of two cluster host nodes per site. This allows for a preferred local
failover in case of a system failure. Local failover operations are faster than a remote failover
between disk arrays because the mirroring direction of the disks does not need to be changed.
XP Cluster Extension can be deployed in environments where several clusters use the same pair of
disk arrays. Although XP disk arrays can be mirrored in various configurations, XP Cluster Extension
does not support multiple disk arrays as both primary and secondary disk arrays. XP Cluster
Extension supports configurations where two or more disk arrays use one remote disk array in a
logical one-to-one configuration.
CAUTION: XP Cluster Extension can operate with only one system at each site, with a single I/O
path between the server system and the disk array and a single link in each direction between
disk arrays.
However, those configurations are not considered highly available, nor are they disaster tolerant.
XP Cluster Extension configurations with single points of failure are not supported by HP.
Consolidated-site configuration
In consolidated-site configurations, a single disk array in the secondary (remote) data center is
connected to up to four other primary disk arrays. For an example of a consolidated-site
configuration, see “Consolidated-site configuration” (page 8). The restrictions outlined in
“One-to-one configurations” (page 7) also apply to consolidated configurations. XP Cluster
Extension does not support configurations in which the application service's data disk set is spread
over two or more disk arrays.
Figure 2 Consolidated-site configuration
Supported Continuous Access configurations and fence levels
The Continuous Access software offers three modes of replication:
• Synchronous replication
• Asynchronous replication
• Journal replication
For the replication modes supported by specific versions of XP Cluster Extension, see the HP SPOCK
website: http://www.hp.com/storage/spock. For information about synchronous and asynchronous
replication modes, see the Continuous Access documentation. For information about journal
replication, see the Continuous Access Journal documentation.
The Continuous Access fence level is used to configure the remote replication feature of an XP disk
array based on your requirements for application service availability, data concurrency, and
8 XP Cluster Extension features