I have had this questions multiple times in the last weeks and decided it was time to get a more official statement out. The question is if VM-Host Affinity rules are supported in a vSphere Metro Storage Cluster (vMSC) environment. The reason people ask this question is because it was explicitly stated to be not supported with vSphere 4.1 and prior. This has changed however.
As of vSphere 5.0 VM-Host Affinity Rules are supported for the configurations which are listed on the vMSC compatibility list. As of writing only EMC VPLEX is officially certified but we are expecting other storage vendors to join them soon. If you are looking to upgrade to vSphere 5 and your storage vendor is not certified yet I would like to suggest contacting one of their representatives and validate if and when they will be certified.
For more details on the EMC VPLEX solution with regards to vSphere 5.0 I would like to suggest reading KB 2007545. (I have requested our KB team to explicitly mention the support for VM-Host affinity rules and hopefully the KB will be updated soon.)
