Hyper-V Clusters – There Are Only 26 Letters In the Alphabet

If you’ve looked at putting Hyper-V in a cluster you might have read Jose Barreto’s blog post on clustering options, viewed Dave Northey’s videos demonstrating it in action or considered trying to recreate what ESX with Virtual Center does.  You’ll soon see that to have failover or mobility on a per-VM basis with Hyper-V on Windows Server 2008, each VM must reside in it’s on disk/LUN on your shared storage.  Windows Server 2008 doesn’t have the ability (yet) to do shared file systems like that in ESX’s VMFS.

You’ll now think … I can have 16 nodes in a cluster and potentially dozens of VM’s in my N+1 or N+2 architecture.  Wait … how many drive letters am I going to need?  I’ve already consumed A, B, C and D … does this mean a cluster can have only 22 VM’s?  This is probably something where some certain-product-fanatic gets to write some blog FUD without digging just a little deeper.  It’s amazing to see how prejudice is tainting the commentary and reviews that are out there right now 🙂

You have the option to use "letterless" drives in Windows Server 2008.  Instead of using a drive letter to identify the physical drive that each VM can reside on, you can use a GUID to identify the drives. 

The only question now is, how do you use these drives?  VirtuallyAware has done a post on the subject.  The hardest part of the process is getting the GUID of the LUN that you’re working with.  Who really wants to type out something nasty like "fc247e42-0a5e-11dd-94db-001b785788b0"?  PowerShell helps at there as the blog post indicates. 

You’ll now have a virtually unlimited set of drive identifiers that will allow your cluster to scale out to the limitations of your CPU, storage and RAM.

On a tangent, this is just another example of where PowerShell is a necessary skill, not only in PowerShell but in all new MS technologies.  I’ve started learning it.  It’s different, that’s for sure, but it’s not optional any longer.

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