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

Figure A-1 Enhanced Distance Cluster Configuration
A.2 Enhanced Distance Cluster Restrictions
Although an Enhanced Distance Cluster provides basic high availability between
remote sites at greater distances, there are additional restrictions necessary to reduce
the volume of data and its latency. Issues and restrictions are as follows:
• The use of the Logical Storage Manager (LSM) to mirror user data or system
disk/data in an Enhanced Distance Cluster configuration is prohibited. LSM can
only be used for striping data in an Enhanced Distance Cluster.
• Only single-instance applications are supported in an Enhanced Distance Cluster
configuration. Multi-instance applications that use the cluster interconnect for
communication between multiple instances, such as ORACLE RAC, are not
recommended in a Enhanced Distance Cluster configuration. This is due to
increased latency on the cluster interconnect. For example, ORACLE RAC uses a
cluster interconnect for its own lock manager traffic and an increase in latency
could lead to unpredictable results.
Additionally, multi-instance applications can increase the burden on the cluster
interconnect and affect inter-member cluster communication so should follow the
configuration recommendations in the next section.
• An Enhanced Distance Cluster should not be used for the following workloads
due to their I/O characteristics and directory locations. (Mail and print usually
keep their data stores in the system directories):
— NFS server
— Mail server
— Print server
A.2 Enhanced Distance Cluster Restrictions 255