Stretched cluster VM & datastore affinity

When using a vSphere stretched cluster solution, it is important to have your VM(s) and its VMDK(s) affinity aligned in the same datacenter. So if the storage controller in datacenter 1 serves the read/write copy of the datastore, you would like the VM to run on a vSphere host in the same datacenter. This will avoid the storage read IO’s to traverse the inter-datacenter connections, resulting in an obvious impact on performance. With the VM – datastore affinity in place, you will also mitigate the risk of potential VM outage if a datacenter partition (aka split-brain scenario) will occur.

Let me show you what I mean by using a simple logical overview of a stretched cluster infrastructure. The following example is based on an uniform storage backend. More information on uniform and non-uniform metro storage solutions is read here.

What you don’t want:

VM affinity

What you do want:

VM affinity


It is perfectly possible to automate the alignment upon… VM creation for example. Needless to say, you will require DRS to run. Preferably in fully automated mode.


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