Building Disaster Recovery Serviceguard Solutions Using Metrocluster with Continuous Access XP P9000 for Linux B.01.00.00
Live Application Detach
There may be circumstances in which you want to do maintenance that involves halting a node,
or the entire cluster, without halting or failing over the affected packages. Such maintenance might
consist of anything short of rebooting the node or nodes, but a likely case is networking changes
that will disrupt the heartbeat. New command options in Serviceguard for Linux A.11.20.10
(collectively known as Live Application Detach (LAD)) allows you to do this kind of maintenance
while keeping the packages running. The packages are no longer monitored by Serviceguard, but
the applications continue to run. Packages in this state are called detached packages. When you
have done the necessary maintenance, you can restart the node or cluster, and normal monitoring
will resume on the packages. For more information on the LAD feature, see Managing HP
Serviceguard A.11.20.10 for Linux available at http://www.hp.com/go/linux-serviceguard-docs.
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 XP or P9000 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 XP or P9000 array.
In a Metrocluster environment with Continuous Access XP or P9000, 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.
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 XP or P9000 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 XP or P9000 external storage feature, through
inter-site replication links. On XP or P9000 array in a Metrocluster site, a command device from
the XP or P9000 array at the remote site is mapped to the local device using the XP or P9000
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 XP or P9000 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 XP or P9000 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.
28 Metrocluster features