Understanding and Designing Serviceguard Disaster Recovery Architectures

Integration with array based replication
Continentalclusters supports array based data replication with HP P9000 or XP ,and HP P6000
or EVA with Continuous Access, HP 3PAR with Remote Copy or EMC with SRDF.
Integration with software based replication
Most database products have a logical replication feature to maintain a redundant copy of the
database. Continentalclusters offers flexibility in terms of integrating software based replication
for disaster recovery. A recovery group can have two optional packages, data sender and data
receiver. The data sender package runs in the primary cluster and the data receiver package runs
in the recovery cluster. Based on the actual software used for replication, either data sender or
data receiver or both must be configured. You can use Data Replication Services toolkit provided
by Serviceguard to integrate Oracle Data Guard and IBM DB2 HADR replication technologies
with Continentalclusters.
Continentalclusters Maintenance mode
On the recovery cluster, recovery groups can be individually moved into maintenance mode.
Continentalclusters does not allow recovery of those recovery groups that are in maintenance
mode, using commands, such as cmrecovercl, or cmrunpkg/cmmodpkg, thus preventing the
recovery package startup.
At initial configuration, by default, all recovery groups are out of maintenance mode. However,
when a recovery group is in maintenance mode the availability of the primary packages are not
impacted. The primary package can start up or can failover locally at the primary cluster.
The maintenance mode can be used for maintenance at the recovery site. This ensures recovery
package does not start up. A typical case when maintenance mode is used is while performing
disaster recovery rehearsal.
NOTE: Maintenance mode is an optional feature. To enable maintenance mode, configure a
shared disk (non-replicated) with a file system on all recovery clusters and the Continentalclusters
configuration file must be specified with the CONTINENTAL_CLUSTER_STATE_DIR.
A recovery group is moved into maintenance mode, by default, only if its primary package is
running. However, if the site is unreachable or primary package is shutdown, you can move a
recovery group into maintenance mode by using the force option.
CAUTION: Do not move a recovery group into maintenance mode, as in the case of the force
option, if it is already recovered. This will prevent subsequent startups of the recovery package.
Also, this will not prevent a rehearsal package startup which could potentially lead to two instances
of application accessing the same data store.
Disaster Recovery Rehearsal
Any disaster recovery process needs auditing to ensure that when a disaster strikes; the
configurations on all the systems, both primary and recovery cluster, are in sync.
The disaster recovery rehearsal is a feature in Continentalclusters that allows the applications in
the recovery side to start up while the applications in the production side continue to run. This
allows an administrator to identify and rectify configuration drift and other issues that may otherwise
prevent an application start-up during recovery.
NOTE: DR Rehearsal startup is allowed only if the recovery group is in maintenance mode. This
is a protection which ensures that while rehearsal is in progress, recovery is prevented. The recovery
and rehearsal package have similar package configuration (that is, share resources), therefore
allowing both of them to start will result in resource collision and impact data integrity.
34 Metrocluster and Continentalclusters