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

Rolling disaster protection
A rolling disaster is a catastrophic event that affects the remote site after an outage at the local site.
In a rolling disaster, data stored on remote disks can be entirely lost during a recovery attempt.
To ensure the survival of critical data during a resynchronization/restore operation, HP StorageWorks
XP Business Copy Software pairs can be associated with the local data disks. XP Cluster Extension
recovers automatically, provided that a local XP Business Copy Software mirror can be suspended.
Although the local copy can be out of date, it represents the best starting point for the recovery.
XP Cluster Extension also resumes local XP Business Copy Software mirrors automatically, if specified,
to allow the local site to keep an up-to-date image of the primary data. To implement rolling disaster
protection, see “Implementing rolling disaster protection” on page 141.
Command-line interface (CLI)
XP Cluster Extension Software provides a CLI to enable disaster tolerance without cluster software.
The CLI is convenient if you use in-house software to migrate application services from one system to
another or if you want XP Cluster Extension to check disk states to make sure you can automatically
start an application service on the local disk array.
Fast Failback using XP Continuous Access Software
XP Cluster Extension supports the XP RAID Manager Fast Failback feature. This feature allows XP
Continuous Access Asynchronous Software to automatically redirect the mirroring direction of a disk
pair even if the remote XP RAID Manager instance is not available. This ensures the fastest possible
recovery to the original site in case of an application service failover at the alternate site.
XP Cluster Extension configurations
XP Cluster Extension is an array-based solution. It requires at least two HP XP disk arrays with XP
Continuous Access Software providing remote mirroring. XP Cluster Extension connects XP software
with cluster software and uses the ability of cluster software to react to system hardware and application
failures.
Servers are members of the same cluster dispersed over two or more sites.
XP Cluster Extension supports one-to-one and consolidated-site configurations.
One-to-one configurations
In one-to-one (1:1) configurations, cluster host nodes are split between two geographically separate
data centers and use redundant, diversely routed network connections for intra-cluster communications.
(See Figure 1 on page 13.) These links must be as reliable as possible to prevent false failover
operations or split-brain situations.
XP Cluster Extension features12