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

Replication Type

How it Works

Continentalclusters Implication

 

 

 

Logical Database Replication

Transactions from the primary

Requirements on CPU and I/O may limit or

 

application are applied from logs to a

prevent the Recovery Cluster from running

 

copy of the application running on the

additional applications.

 

recovery site. (This is an example only;

 

 

there are other methods.)

 

 

 

 

Logical Filesystem

Writes to the filesystem on the primary

CPU issues are the same as for Logical

Replication

cluster and are duplicated periodically

Database Replication. The software may have

 

on the recovery cluster.

to be managed as a separate Serviceguard

 

 

package.

 

 

 

Physical Replication of Data

Disk mirroring via LVM software.

Requirements on CPU are less than for logical

Volumes via Software

Mirroring is done on disk links (SCSI or

replication, but there is still some CPU use.

 

FibreChannel).

Distance limits may make this type of

 

 

 

Designing a Disaster Recovery Architecture for use with Continentalclusters

49