Ah, the lovely feeling inside when you start to plan a Hyper-V environment with servers, clusters, network and storage. 🙂 There are so many things to think about, to plan, to set up, to test and to fix. In the enterprise Hyper-V in Windows 2008 came really short in my honest opinion since it was a pain to cluster. As you may know, cluster nodes are assigned storage in LUNs, and only one node can access any given LUN at the time. This means that when you store virtual machines and their data on a LUN then you have to migrate everything on the LUN from one node to another node when you migrate the virtual machine. So to make the virtual machines independent of each other you have to make a separate LUN for every single virtual machine in the cluster! At only 50 virtual machines the administrative tasks are getting a little out of hand.
But in Windows 2008 R2 we got CSV which is short for Cluster Shared Volumes (not comma separated values). This is a new cluster storage type which simply enables several virtual machines to access their VHD files on the same LUN and still operate, or move between, different cluster nodes independently. That’s the basic desciption and there are more detailed information here: http://technet.microsoft.com/en-us/library/ff182346(WS.10).aspx
Some benefits include
- You need far less LUNs (obviously)
- Every LUN needs some space to allow for datagrowth in the virtual machines. With fewer LUNs you’ll make much better use of your available storage space
- The path to the CSV is stored under the folder \ClusterStorage under the systemdrive and it’s the same path regardless of which node you’re looking from. So tracking the paths are easier now
- Virtual machines can still fail over and move between cluster nodes independently
- You can set up some clever designs, for example where the system drives, data drives and page files to the virtual machines are placed on separate physical sotage solutions (and LUNS) for performance gains without having to implement a jungle of LUNs.
CSV are available in all editions of Windows Server 2008 R2 that includes Failover Clustering, as well as Hyper-V Server 2008 R2. Also notice that putting other clustered resources on CSV is not support, it’s for virtual machines only.