HP Tru64 UNIX and TruCluster Server Version 5.1.B-4 Patch Summary and Release Notes (13156)

• If a site disaster occurs that involves multiple failures, high availability will be lost. Therefore,
there needs to be procedures in place for the manual rebooting of the surviving site. The
surviving site will work as a normal cluster with minimal or no data loss.
• A single, combined span of up to 100 km using three switches and two segments of 50 km.
• The configuration must have at least one physical subnet to which all cluster members and
the default cluster alias belong.
• The cluster must have an extended, dedicated cluster interconnect to which all cluster
members are connected to serve as a private communication channel between cluster
members. The interconnect must be shielded from any traffic that is not a part of the cluster
communication according to the requirements for the LAN based cluster interconnect in the
TruCluster Cluster Hardware Configuration manual.
Figure A-1 provides an example of an Enhanced Distance Cluster cluster interconnect
configuration. The nodes at Data Center 1 are connected to a switch that is connected to an
intermediate switch using a fiber link of up to 50 km. From the intermediate switch, another
fiber link of up to 50 km connects to a third switch, to which the remaining two nodes at Data
Center 2 are attached, thereby, establishing an overall distance between the sites of up to 100 km.
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.
184 Setting Up an Enhanced Distance Cluster