Summary of failure scenarios

Failure	Reported with	Operation interrupted?	Impact	Response (measure)	Data inconsistency on later switch to targets?
source unit	NDE0020	No	Local redundancy	Customer support	No
target unit	NDE0020	No	Remote redundancy	Customer support	No
Single remote link	NDE0019	No	Write performance	Customer support	No
Last remote link	NDE0019	No	-	Customer support Note inconsistency	Yes
Storage system with source units	PGER message	Yes		Measure A	Possible 1
Local system	–	Yes	-	Restart	No
Complete failure 2	–	Yes		Measure A	Possible 1
Failback to local storage system	–	Yes		Measure B

¹ Data inconsistency on later switching to the targets is possible in the event of preceding faults on the remote links or target units.

² Failure of the local storage system with source units and failure of the local system.

Failure recovery measures

Measure	Description	Condition	Action	Command
A	Switch to target unit, local system affected		Start standby host, attach target units	/ATTACH-DEVICE
		Source and target units were synchronized	Make target units available	/HOLD-REMOTE-COPY
		Source and target units were not synchronized, inconsistencies acceptable (or reset to last synchronization point)		/HOLD-REMOTE-COPY ...,   FORCE=YES
B	Failback to the local storage system, operation on standby host		Terminate use of target units	/EXPORT-PUBSET
			Disable all channels and remote links on local storage system	(Service)
			Start local storage system	(Service)
		Local storage system OK (Service will check)	Attach and enable remote links	(Service)
			reconstruct source units from target units	/RESUME-REMOTE-COPY   RESTORE=*TO-SOURCE or in single steps
		Comparison OK / automatic synchronization begun?	Attach channels	(Service)
			Start local system