For a high availability, Availability Resources are often grouped together in one of these flavors:
- Availability Resources are redundant, i.e. multiple Availability Resources exist that can do the same work and one can backup another in case it fails;
- Availability Resources go together where one is depicted as the primary Availability Resource and the other is depicted as the secondary Availability Resource.
Examples:
- Ten IMS Message Processing Regions that are configured to serve the same IMS shared queue, for example, can be considered redundant Availability Resources where nine regions can compensate potentially the failure of a single region. Or, a SAP Central Services region is in charge to provide SAP services in a cluster of systems. Another standby copy of such a region can take over the responsibilities of the primary central services region, should the primary fail or become degraded. Both are examples of redundant Availability Resources grouped in a Redundancy Group.
- A storage disk can be mirrored synchronously or asynchronously to another secondary disk. The I/O is always driven on the primary disk and declared complete, when the data is also either copied to the secondary disk or safely accepted for copy. In this example, both disks are in a Replication Group. In case the primary disk fails or it can no longer reached, I/Os can be switched to the secondary disk. Depending on the replication method, the data on the secondary disk can be identical (no loss of data) or lack behind a few seconds.
A consumer will be able to inspect Availability Resources that themselves are representing groups of redundant Availability Resources or replicated Availability Resources. The consumer can understand the individual members and their roles in such groups. It also can use this information to monitor the level of redundancy in a group.
As a pre-requisite, the consumer has obtained a list of all Availability Resources from the service provider, so that he understands the workloads that can be automated and which of them provide redundancy because they represent groups containing other Availability Resources as a member. See also scenario Obtain list of workloads
Steps
- The consumer is given the service provider to use.
- The consumer knows that the Availability Resource provides redundancy.
- The consumer requests a list of members for such an Availability Resource with their status and their role as seen by the service provider. An overall redundancy status is provided as well.
Variations
None.
Example
A system administrator wants to bring down all applications of server ABLE which also affects the PAYROLL business application. By using this scenario, he will get an immediate understanding whether shutting down ABLE causes an outage for PAYROLL. If there is redundancy for PAYROLL, he can safely stop ABLE or perform a planned failover (see also Failover a workload) of PAYROLL to BAGLE or CHARLY, for instance.
