Disaster Tolerance and Recovery in a Serviceguard Cluster

Understanding Types of Disaster Tolerant Clusters

Cluster Extension (CLX) Cluster

A Linux CLX cluster is similar to an HP-UX metropolitan cluster and is a cluster that has alternate nodes located in different parts of a city or in nearby cities. Putting nodes further apart increases the likelihood that alternate nodes will be available for failover in the event of a disaster.

The architectural requirements are the same as for an extended distance cluster, with the additional constraint of a third location for arbitrator node(s) or quorum server. And as with an extended distance cluster, the distance separating the nodes in a metropolitan cluster is limited by the data replication and network technology available.

In addition, there is no hard requirement on how far the third location has to be from the two main data centers. The third location can be as close as the room next door with its own power source or can be as far as in a site across town. The distance between all three locations dictates the level of disaster tolerance a metropolitan cluster can provide.

On Linux, the metropolitan cluster is implemented using CLX.

•CLX for XP

•CLX for EVA

For HP-UX, Metropolitan cluster architecture is implemented through the following HP products:

•Metrocluster with Continuous Access XP

•Metrocluster with Continuous Access EVA

•Metrocluster with EMC SRDF

The above HP-UX products are described in detail in Chapters 3, 4, and 5 of the Designing Disaster Tolerant HA Clusters Using Metrocluster and Continentalclusters user’s guide. The Linux products are described in detail in Getting Started with MC/ServiceGuard for Linux guide. While there are some differences between the HP-UX and the Linux versions, the concepts are similar enough that only Cluster Extension (CLX) will be described here.

On-line versions of the above document and other HA documentation are available at http://docs.hp.com -> High Availability.

On-line versions of the Cluster Extension documentation is available at

http://h71028.www7.hp.com/enterprise/cache/120851-0-0-225-12

1.html-> HP StorageWorks Cluster Extension EVA or XP.

Chapter 1

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