When designing vSphere clusters, vSAN or not, its pretty common knowledge that the hardware should match as much as possible. This includes the server make and model, CPU/RAM configuration, HBA, disks, NICs etc. There are times when this is not possible, or doesn’t make sense. Examples would be when the servers in your cluster are EOL or you know they will be soon and you would rather purchase the newer server generation than buy hardware that will soon not be supported by the manufacturer.
I recently asked my local vSAN SE if VMware had an official stance regarding mixing server or CPU generations in a vSAN cluster. His response was that he certainly wouldn’t recommend it but he stopped short of saying mixed configurations would not be supported. We didn’t have enough time to discuss further so I basically walked away with the attitude that I would have to ensure that whenever I was designing a vSAN cluster for a customer I would ensure that I was using hardware that they would be able to easily duplicate for the next few years should they have the need to expand their cluster.
Fast forward to this week when this question was brought up by another individual on the vExpert Slack channel and it cause a bit of a debate. Several of us were discussing this and we basically came to the conclusion that we could not find an official VMware stance on this. Some of the documentation found on storagehub.vmware.com gave some guidance but nothing definitive.
So assuming you can keep everything the same aside from CPU/motherboard does vSAN care? The conclusion we came to during this discussion is that as long as you are using EVC then vSAN shoudln’t care. It is certainly considered best practice to keep hardware identical whenever possible. It is important to be mindful when mixing CPUs that vSAN will essentially be bound by your weakest CPU when serving IOs in this type of scenario.
During the conversation a couple of VMware employees chimed in and confirmed that as long as you are keeping CPU/RAM/Storage balanced accross hosts in the cluster, it shouldn’t matter. There was even an implication that this is officially documented somewhere but I have not been able to find any source for this as of yet.
Bottom line, when expanding a vSAN cluster keep the hardware identical if possible. When its not possible pay close attention to the hardware in the new hosts and make it as balanced as possible.