I have been hearing a lot of interest from my clients lately about stretched vSphere clusters. I can certainly see the appeal from a simplicity standpoint. At least on the surface. Let’s take a look at the perceived benefits, risks, and the reality of stretched vSphere clusters today.
First, let’s define what I mean by a stretched vSphere cluster. I am talking about a vSphere (HA / DRS) cluster where some hosts exist in one physical datacenter and some hosts exist in another physical datacenter. These datacenters can be geographically separated or even on the same campus. Some of the challenges will be the same regardless of the geographic location.
To keep things simple, let’s look at a scenario where the cluster is stretched across two different datacenters on the same campus. This is a scenario that I see attempted quite often.
This cluster is stretched across two datacenters. For this example let’s assume that each datacenter has an IP-based storage array that is accessible to all the hosts in the cluster and the link between the two datacenters is Layer 2. This means that all of the hosts in the cluster are Layer 2 adjacent. At first glance, this configuration may be desirable because of its perceived elegance and simplicity. Let’s take a look at the perceived functionality.
- If either datacenter has a failure, the VM’s should be restarted on the other datacenter’s hosts via High Availability (HA).
- No need for manual intervention or something like Site Recovery Manager
Unfortunately, perceived functionality and actual functionality differ in this scenario. Let’s take a look at an HA failover scenario from a storage perspective first.
- If …
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