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bakura
Contributor
Contributor

Does SRM depend on write order consistency guarantee by underlying storage replication

In order for SRM to work correctly in a disaster recovery sitation, does it depend on the underlying storage unit replication to guarantee write order consistency?

When I perform a failover, it look like a snapshot of the production vmfs volume is used in the recovery site. If the recoery site is using the most recent valid snapshot, I presume it is being created periodically in the production site while the mirror is in operation, and if the recovery site can validate the integrity of the snapshot without relying on the sequental consistency (write order) being preserved by the storage replication system, it seems to me that there is no need to enable sequential consistency in the hardware replicaiton.

Storage replication will give better performance (in terms of less impact to the production response time as well as the copy throughput) if there is no need to maintain sequential consistency.

If the above is true, doest it also apply in case of V-RDM (Virtual Raw Device mode) as well as P-RDM (Physical RDM) in addition to VMFS?

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Jay_Judkowitz
Enthusiast
Enthusiast

Bakura,

I'm not sure I follow the question 100% so please let me know if this helps or if you need me to take this in a different direction.

Basically, SRM does not impose any requirements on your replication other than that the replication is covered in the compatibility guide. So, you can set up replication that:

  • Is snapshot based or continuous

  • Is synchronous or asynchronous

  • Preserves write order consistency across LUNs or does not do so

  • Ties in application consistency to the replication or does not.

    • App consistency generally requires snapshot based replication, not continuous

    • App consistency generally requires physical compatibility mode RDMs, but some arrays can do it on VMFS as well.

So, your decision on how to setup replication should be completely based on

  • Price/performance tradeoffs

  • Needs around app consistency

  • Needs around multi-LUN consistency

  • Bandwidth available, data change rate, frequency you change the same blocks of data

SRM should not be a limiting factor for your choice of replication configuration. The exception to this rule is that SRM does not support replication topologies beyond 1:1 mapping of LUNs at source and destination site - we don't support replicating 1 LUN to two different LUNs. (I'm sure that's outside the scope of your question, but I just wanted to make sure I was being 100% complete and accurate for anyone else reading this.)

Thanks,

Jay