In failure scenarios it is first necessary to determine whether data is mirrored using REC or whether a concurrent remote copy configuration is in use.
This section deals with the most important failure scenarios without concurrent remote copy. In concurrent remote copy configurations the scenarios and measures apply analogously, but the following general conditions should also be taken into account when deciding on the measures:
In the event of local failures, a decision must be made as to which of the two standby systems is to continue operation.
In the event of failback, concurrent remote copy replication must also be resumed on both standby systems.
The general conditions of the SWAP-REMOTE-COPY functionality must be observed.
The following failure scenarios and measures for maintaining operation will be examined:
"Failure of the local storage system and of the local system" (complete failure)
"Failure as a result of failback to the local storage system"
After a storage system failure or a different failure in the local system, a check should be carried out to establish whether local troubleshooting can recover the application faster
than remote recovery. In many cases local troubleshooting is quicker.
If remote recovery is performed, you must consider the application downtime involved in switching to the standby system, starting the application there, and then switching back to the local system once the problem has been resolved.
In addition to the failure scenarios under SHC-OSD examined here, further functions for enhancing availability are provided with storage cluster option or by means of live migration.