HP Tru64 UNIX and TruCluster Server Version 5.1B-5 Patch Summary and Release Notes (March 2009)

A.3 Enhanced Distance Cluster Recommendations
Although Enhanced Distance Cluster configurations provide access from both sites to
all shared data storage in the system, the volume of traffic to off-site storage, either
through the storage or cluster inter-site connections, should be minimized to maintain
performance levels. Therefore, you should be aware of the following recommendations
are applicable. Not following these recommendations can have detrimental effect on
system performance and availability.
The main purpose of most of these recommendations is to design a configuration that
minimizes I/O latency and contention issues within both the cluster and the SAN storage
inter-site connections:
• The configuration of an application and its data storage should be located within
the same site. Doing otherwise can cause significant performance degradation to
the application’s runtime performance.
• Each application should have its associated data in separate file systems, or AdvFS
domains, in order to locate the CFS server for these file systems with the application.
• Applications should not use any storage/directory within the system tree (for
example, root, /usr, /tmp, /var, /var/tmp, and so on). Instead they should use
dedicated file systems that can be co-located with the application. If the application
requires a directory in the system tree, a symbolic link should be used to redirect
these directories to a separate storage/file system.
• The use of remote I/O via DRD to serve devices is strongly discouraged due to the
increased traffic on the cluster interconnect possibly resulting in unacceptable
latencies.
• Although the use of LSM for striping is supported, it is not recommended for use.
• Although data replication is supported between HSG80 arrays, their use as shared
storage within an Enhanced Distance Cluster it is not recommended. This is due
to the inter-site distance limitations of the HSG80's remote data replication, which
would significantly impact the Enhanced Distance Cluster configuration.
• The use of a cluster alias for network-client access is discouraged due to the
potential for additional traffic on the cluster interconnect if the alias router is not
located with the application.
If a cluster alias is used, each application must have its own cluster alias. Each
application should have its cluster alias router located on the node where the
application is executing. This can be achieved by using the cluamgr command
and adjusting the values of selection weight and routing priority. During a failover
of the application, the cluster alias also should be relocated to the same node.
256 Setting Up an Enhanced Distance Cluster