HP StorageWorks XP Cluster Extension Software Administrator Guide (T1656-96035, April 2010)

Figure 1 One-to-one (1:1) configuration
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Each cluster host node needs redundant FC or SCSI I/O paths to the XP disk array. Individual hosts
cannot be connected to both the primary (P-VOL) and the secondary (S-VOL) copy of the application
disk set.
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 XP
disk arrays because the mirroring direction of the XP disks does not need to be changed.
XP Cluster Extension can be deployed in environments where several clusters use the same pair of XP
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 XP disk array in the secondary (remote) data center is
connected to up to four other primary XP disk arrays (see Figure 2 on page 14.) The restrictions
outlined in “One-to-one configurations” on page 12 also apply to consolidated configurations. XP
XP Cluster Extension Software Administrator Guide 13