One of the strengths of Hyper-V is one of its weaknesses: it supports a huge variety of hardware including hosts and storage. Hyper-V clusters need to be treated like mainframes. Any change, no matter how small you think it is, needs to be verified and tested (by somebody) before you apply it. We typically advise people with a Hyper-V cluster not to update drivers, firmwares, etc, unless they have to. And if they do, then they need to work with hardware vendors to ensure that they are tested with the build of Hyper-V and that the various updates are regression tested. For example, blades with SAN cannot have just one firmware updated: an entire set of firmwares and drivers must be deployed.
And along comes SP1 for Windows Server 2008 R2. All those integrated hotfixes and Dynamic Memory are really tempting, aren’t they? Wouldn’t you just love to deploy it as a part of your standard host build?
Question: do your server and storage vendors support SP1 yet? Are your drivers tested on SP1 by the h/w vendor? Is your storage going to work if you deploy it? Will your cluster validation (required for MS support) work after you install SP1? Will you need firmware updates before you deploy the service pack? Have you asked these questions yet?
Make sure that your storage and server vendors do support W2008 R2 SP1 and that your firmwares and drivers versions meet the requirements before you install the SP. You don’t want to finish that last reboot and get a nasty surprise when you re-run the cluster validation or run a storage level backup of your CSVs.