Designing Disaster Recovery Clusters using Metroclusters and Continentalclusters, Reprinted October 2011 (5900-1881)

Remote Array RAID Manager Instance
A remote array RAID Manager instance allows the Metrocluster package to determine the status
of the device group on the remote P9000 or XP array even when the remote hosts are down or
are inaccessible due to a network link failure. The remote array RAID Manager instance is configured
on a node using the command device of the remote P9000 or XP array.
In a Metrocluster environment with Continuous Access P9000 or XP, the array at each site is
interfaced only with the Metrocluster nodes in the same site using a command device in the array.
When a Metrocluster package starts up on a node, the RAID Manager instance in the site
communicates with the RAID Manager instance at the remote site to obtain the Continuous Access
device group status. In situations where the remote hosts are down or are inaccessible due to a
network link failure, the Continuous Access device group status cannot be determined. This occurs
even when the remote array is up. Since data currency cannot be determined, the Metrocluster
package startup fails for packages that have the AUTO_NONCURDATA parameter set to 0. Even if
the package is started using FORCEFLAG, the P9000 or XP Continuous Access replication is
suspended when the fence level is set to never.
Similarly, in a 2-node Metrocluster configuration that has a single node at each site, any node
failure results in the other node not being able to determine the device group status. The subsequent
failover of the Metrocluster packages to the surviving node may not succeed either.
In these situations, the remote array RAID manager instance allows the Metrocluster package to
determine the device group status and start successfully. The remote array RAID Manager requires
access to a command device configured on the remote array. Access to this command device at
the remote array can be configured using one of the following methods:
• Using the P9000 or XP external storage feature (Remote Command Device)
A Remote Command Device (RCMD) is a device to which a command device in a remote XP
array is mapped. The RCMD is configured using the P9000 or XP external storage feature,
through inter-site replication links. On P9000 or XP array in a Metrocluster site, a command
device from the P9000 or XP array at the remote site is mapped to the local device using the
P9000 or XP external storage feature. The mapped command device is then presented to the
nodes in the site to be used as a remote command device. This RCMD configuration is done
between arrays on both sites in a mutual fashion. For more information on the behavior of the
command device of a remote P9000 or XP array, see the HP StorageWorks P9000 External
Storage for Open and Mainframe Systems User Guide or HP StorageWorks XP External
Storage user guide available at the following location:
http://bizsupport1.austin.hp.com/bizsupport/TechSupport/ProdSearch.jsp?
prod=HP%20StorageWorks —> HP StorageWorks XP Array Manager Software —> Manuals.
• Using extended SAN
The dedicated command device from the P9000 or XP array in the remote site is directly
presented to the nodes in the local site over an extended SAN. This configuration does not
use the XP external storage feature.
HP recommends configuring a remote array RAID Manager instance in all Metrocluster
configurations, especially in a 2-node configuration, as it is more robust. For more information on
configuring a remote array RAID Manager instance in Metrocluster, see “Configuring a remote
array RAID Manager instance” (page 170).
NOTE:
• Remote command device can be configured in Continentalclusters.
• Remote command device need not be configured when P9000 or XP Continuous Access
Journal replication is used.
158 Building Disaster Recovery Serviceguard Solutions Using Metrocluster with Continuous Access for P9000 and XP