When I was looking in to vSphere Flash Read Cache (part of vSphere 5.5) there was one thing that had my interest, how does it interact with vSphere HA and DRS and more specifically, are there any caveats? It all started with the question what are the requirements for a virtual machine to be successfully restarted by vSphere HA?
The answer was simple, when you define a vSphere Flash Read Cache size for a virtual disk on a virtual machine, that amount of cache capacity defined for that virtual disk needs to be available on a local flash resource in order for the VM to be restarted / powered-on. So what does this mean? Well it means that when you set a flash read cache for a given virtual disk to 4GB, that 4GB needs to be available on your local host where the VM will be powered on. But what in the case of an HA initiated restart? Will HA ignore this requirement during restarts or will it try to guarantee the same performance? [Read more…] about Something to know about vSphere Flash Read Cache