HP XP Continuous Access Software - Manual (Page 23)

Description 23
RAID Manager instances
Each execution of RM is known as an RM instance. Instances are local or
remote and can run on the same host or different hosts. Two RM instances
are typically required to manage BC or CA pairs.
Local instance The RM instance currently being used, that is, the
instance to which commands are issued. Local
instances link to remote instances by using UDP socket
services.
Remote instance The RM instance that the local instance communicates
with, as configured in the HORCM_INST section of
an RM instance configuration file. (For further
information on the RM instance configuration file see
page 41 )
There are four possible RM topologies:
• One host connected to one disk array
If you are using one host, both RM instances are located on the same
host.
• One host connected to two or more disk arrays
Using a single host connected to two or more disk arrays allows you to
maintain duplicate data on two different disk arrays. When you choose
this option, the host Logical Volume Manager must not be able to see
both sides of the same BC or CA pair or it will become confused.
• Two or more hosts connected to one disk array
Using two hosts connected to one disk array allows you to locate one
RM instance on each host and thus maintain separate copies of the
data controlled by independent hosts; primary volumes (P-VOLs) are
used by one host while secondary volumes (S-VOLs) are used by the
other host (for example, for backup, testing, or data duplication).
• Two or more hosts connected to two or more disk arrays
Using two or more hosts connected to two or more disk arrays allows
the most flexible CA disaster recovery plan. The remote and local sets