Cascading Failover in a Continentalclusters, December 2005

dictated by the frequency at which it is refreshed (that is data replicated from primary site to recovery
site). The refresh process is shown in Figure 4.
Figure 4 - Data Refresh in Steady State
The following procedure describes the steps necessary to periodically copy the data from the
secondary disk array to the recovery disk array while the application is running on the primary site.
1. Freeze the application I/O to prevent the application from writing data to the primary
devices in the primary disk array. Note, the method of freezing the I/O is application
dependent.
2. Make sure that data has replicated to the remote site before executing the next step.
3. Split the local mirror devices (device B’) in the secondary disk array from the primary
replication group.
4. Resume the application I/O to the primary devices in the primary disk array if needed. Note,
the method of resuming the I/O is application dependent.
5. Split the local mirror devices (device C’) in the recovery disk array from the secondary
replication group. This is required to preserve an old copy of the data just in case a failure
occurs during data synchronization between the secondary disk array and the recovery disk
array that may cause data corruption on the destination devices in the recovery disk array.
6. Incrementally establish the secondary replication group (i.e. group between the secondary
disk array and the recovery disk array). The data is copied from secondary disk array local
mirror devices (device B’) to the recovery disk array secondary devices (device C).
7. Wait until the copying has completed before continuing to the next step.
8. Once the copy completes, split the data replication link between the secondary disk array
and the recovery disk array.
9. Re-establish the local mirror devices (device C’) in the recovery disk array as mirrors of the
secondary devices.
10. Re-establish the local mirror devices (device B’) in the secondary disk array as mirrors of the
secondary devices of the primary replication group.
Package Setup
Except for the following package setup instructions, packages for both primary and recovery follow
the same steps as setting up a Continentalclusters package. See the Designing Disaster Tolerant High
Availability Clusters manual for more information on setting up packages.
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