User's Guide

NOTE: Take note when cluster A takes over for cluster B, it must run cluster B’s packages as well
as any packages that it was already running on its own, unless those packages are stopped
intentionally.
Data Replication
Data replication between the Serviceguard clusters in a Continentalclusters recovery pair extends
the scope of high availability to the level of the Continentalclusters. Select a technology for data
replication between the two clusters. There are many possible choices, including:
• Logical replication of databases
• Logical replication of file systems
• Physical replication of data volumes via software
• Physical replication of disk units via hardware
Table 9 is a brief discussion of how a data replication method affects Continentalclusters
environment.
Specific guidelines for configuring the HP StorageWorks P9000 Disk Array family or HP
StorageWorks XP Disk Array series, HP StorageWorks Disk Array EVA Series, and the EMC
Symmetrix Disk Array or HP 3PAR Storage Systems for physical data replication in
Continentalclusters are provided in Chapters 3, 4, 5, and 6. To use these data replication solutions
in a Continentalclusters environment it is necessary to purchase either the Metrocluster with
Continuous Access for P9000 and XP, or Metrocluster with Continuous Access EVA, or Metrocluster
with EMC SRDF, or Metrocluster with 3PAR Remote Copy products separately.
If a data replication technology is chosen that is not mentioned above, and if the integration is
performed independently, then it is necessary to use the guidelines described in section, “Using
the Recovery Command to Switch All Packages” (page 95). In that case, note the following:
• Continentalclusters product is only responsible for the following: Continentalclusters
configuration and management commands, the monitoring of remote cluster status, and the
notification of remote cluster events.
• Continentalclusters product provides a single recovery command to start all recovery packages
that are configured in the Continentalclusters configuration file. These recovery packages are
typical Serviceguard's packages. Continentalclusters recovery command does not do any
checking on the status of the devices and data that are used by the application prior to starting
the recovery package. The user is responsible for checking the state of the devices and the
data before executing Continentalclusters recovery command.
Table 9 Data Replication and Continentalclusters
Continentalclusters ImplicationHow it WorksReplication Type
Requirements on CPU and I/O may limit or
prevent the Recovery Cluster from running
additional applications.
Transactions from the primary
application are applied from logs to a
copy of the application running on the
Logical Database Replication
recovery site. (This is an example only;
there are other methods.)
CPU issues are the same as for Logical
Database Replication. The software may have
Writes to the filesystem on the primary
cluster and are duplicated periodically
on the recovery cluster.
Logical Filesystem
Replication
to be managed as a separate Serviceguard
package.
Requirements on CPU are less than for logical
replication, but there is still some CPU use.
Disk mirroring via LVM software.
Mirroring is done on disk links (SCSI or
FibreChannel).
Physical Replication of Data
Volumes via Software
Distance limits may make this type of
Designing a Disaster Recovery Architecture for use with Continentalclusters 49