A few tidbits on vSphere Replication

A few quick things about vSphere Replication:

  • It comes at no cost, incorporated into vSphere 5.1 onwards and uses the hypervisor to replicate VM’s over the network. There’s a gotcha here though, it uses the management network for replication. In case you want it to use a different vSwitch/vDS to replicate data, read this article. Great read!
  • A great thing about it is being hardware agnostic, you can make it replicate VM’s living on FC storage to your DR site that uses iSCSI storage or vice-verse. You can also replicate from say EMC FC storage to Starwind iSCSI storage. So it’s both hardware and protocol independent. Great for testing and for folks that dont have modern-day arrays or have relaxed RPO times.
  • Microsoft Volume Shadow Copy Service can be used to quiesce apps for consistency. Multiple Point-in-time replication can also be configured to roll back to a known good state. For example, you had a database VM that was having its vmdk’s replicated and there was a problem at say the 5th PIT snapshot and data got corrupted. Subsequent replications will also be corrupt as a result. Having PIT snapshots lets you roll back to the 4th snapshot and you are back in business.
  • There’s a performance hit associated with using vSphere Replication. Besides, the best RPO you can have is 15 minutes. If you want to go any quicker, array-based replication is your only solution. With a 15 minute RPO, you understand that you can sustain a loss of 15 minutes of data.
  • RDM’s and FT VM’s arent yet fully supported. Only vRDM’s are supported and the snapshot hierarchy is not replicated.
  • Your powered-ff VM’s arent replicated which is kind of obvious because if they arent powered-on ESXi cant detect any changes and cant replicate anything.
  • No automated failback! Some customers assume vSphere Replication comes with automated failback. Wrong, it doesnt – but it does support manual failback.
  • DO NOT use vSphere Replication for AD Domain Controllers!! Test it out in a test lab and see what happens to your AD if you turn on the recovered VM’s in the recovery site.
  • You can use a mix of vSphere Replication and array-based replication. A previous employer had their branch offices replicating to the main site using vSphere Replication and the main site to the recovery site using array-based replication.

For more great info, read this VMware kb article.

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