Failover difference with SRM4 and SRM5 on HDS VSP

This blog post highlights the technical difference on how vCenter SRM4 and SRM5 do failover with Hitachi’s Virtual Storage Platform (HDS VSP). Credits to Saravanan Mahalingam for delivering this information.

SRM 4

  • SRM4 does not support failback operation
  • SRM4 uses horctakeover command for failover operation. Horctakeover command fails over to remote site and reverses the replication automatically when the volumes are in PAIR status and the remote array is online (in order to make sure the horctakeover command succeeds for TrueCopy sync, fence level of data must be used).
  • When the horctakeover command fails to reverse the replication, the S-VOL is kept in a special state called SSWS. In order to reverse the replication, pairresync -swaps must be executed manually.

 SRM 5

  • SRM5 introduced re-protect and failback operations
  • SRM5 uses pairsplit –RS command for failover operation. Hence the status of S-VOL will always be in SSWS state after the failover
  • Re-protect operation uses the pairresync command to  reverse the replication and make the volumes in PAIR state (S-VOL to the P-VOL and resynchronized the NEW_SVOL based on the NEW_PVOL)
  • Failback/personality swap operation uses the pairresync –swaps command to reverse the replication

So  while SRM4 is reversing the replication automatically, SRM5 needs the “manual” Re-protect option for that. This is important to know in case you need to guarantee replication before VM’s get booted on the Recovery Site (as part of the run book).

For more information on how to implement HDS VSP with vCenter Site Recovery Manager 5 see these resources:

 

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