We are currently running an IBMi applicaiton connected to a V5030 SAN, replicating over FC to a remote V5030 using Metro Mirror managed by CSM,

We are trying to understand what might happen if the remote SAN fails (the primary possibility being a remote data centre power failure in which power to the SAN directors goes off) and so the SAN is not able to perform a remote write.  Will the write fail and produce an application or system error on IBMi or is there an option in the SAN to continue the local write when it cannot perform the remote write and issue an error message

Hi Laurence,

If the remote system fails, the partnership link will go offline and all the relationships, consistency groups will  stop. During this time all host writes will still be completed at the primary, and a bitmap will record what has become our of sync at the DR site.

When the system and partnership are recovered, the out of sync data will be sent to the DR site using the background copy process. The DR will be inconsistent during the catch up period. 

The primary site applications will continue to accept read and writes throughout, there maybe a slight latency blip at the time the partnership goes offline.

Hello Laurence.  

To add to Barry's answer, your current local IBMi server/application will be error free of this remote failure since the v5030 is handling the replications in the background.  The v5030 system will complain it lost its partnership and will notify on the consistency group going offline.  When it all comes back online, your remote data will recover the changes from the buffered IO on the local system.

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Stephan Durand
Manager Information Technology – Storage & Backups, Disaster Recovery & Infra *NIX / IBMi

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