Disaster Tolerance and Recovery in a Serviceguard Cluster
Managing a Disaster Tolerant Environment
Even if recovery is automated, you may choose to, or need to recover from some types of disasters with manual recovery. A rolling disaster, which is a disaster that happens before the cluster has recovered from a previous disaster, is an example of when you may want to manually switch over. If the data link failed, as it was coming up and resynchronizing data, and the data center failed, you would want human intervention to make judgment calls on which site had the most current and consistent data before failing over.
•Who manages the nodes in the cluster and how are they trained?
Putting a disaster tolerant architecture in place without planning for the people aspects is a waste of money. Training and documentation are more complex because the cluster is in multiple data centers.
Each data center often has its own operations staff with their own processes and ways of working. These operations people will now be required to communicate with each other and coordinate maintenance and failover rehearsals, as well as working together to recover from an actual disaster. If the remote nodes are placed in a
Rehearsals of failover scenarios are important to keep prepared. A written plan should outline rehearsal of what to do in cases of disaster with a minimum recommended rehearsal schedule of once every 6 months, ideally once every 3 months.
•How is the cluster maintained?
Planned downtime and maintenance, such as backups or upgrades, must be more carefully thought out because they may leave the cluster vulnerable to another failure. For example, nodes need to be brought down for maintenance in pairs: one node at each site, so that quorum calculations do not prevent automated recovery if a disaster occurs during planned maintenance.
Rapid detection of failures and rapid repair of hardware is essential so that the cluster is not vulnerable to additional failures.
Testing is more complex and requires personnel in each of the data centers. Site failure testing should be added to the current cluster testing plans.
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