Building Disaster Recovery Serviceguard Solutions Using Metrocluster with Continuous Access for P9000 and XP A.11.00

Both these configurations protect the VM environment from disasters that result in the failure of an
entire data center. For more information on the configuration, see the white paper Implementing
disaster recovery in virtualized environment using HP vPars and HP Integrity VM with Metrocluster
and Continentalclusters on HP-UX 11i available at http://www.hp.com/go/hpux-serviceguard-docs
—> HP Serviceguard Metrocluster with Continuous Access for P9000 and XP.
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 every 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 currentness of data cannot be determined, the Metrocluster
package startup fails for packages that have the AUTO_NONCURDATA parameter set to 0. For
more information on AUTO_NONCURDATA parameter see “Package attributes for Metrocluster
with Continuous Access for P9000 or XP” (page 161).
Similarly, in a 2-node Metrocluster configuration that has a single node at every 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 might 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 about the behavior of the command device
of a remote P9000 or XP array, see HP StorageWorks P9000 External Storage for Open and
Mainframe Systems User Guide available at http://www.hp.com/support/manuals -> storage ->
Storage Software -> Storage Device Management Software -> HP P9000 External Storage Software
or HP StorageWorks XP External Storage user guide available at http://www.hp.com/support/
manuals -> storage -> Storage Software -> Storage Device Management Software -> HP XP External
Storage Software.
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
about configuring a remote array RAID Manager instance in Metrocluster, see “Configuring a
remote array RAID Manager instance” (page 56).
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