Configuring LUNs for virtual machines

Two nice folks responded to my post on the VMTN forums regarding how to set up VMFS partitions and LUNS for virtual machines on our SAN.

Before I talk about all of this, Stephan Stelter from LeftHand Networks also included a link about "How to Align Exchange I/O with Storage Track Boundaries". Good to know...

But anyway, this is apparently what most people do:

• Create VMFS partitions for system drives, and place virtual machines that you would back up together on the same LUN.
• For data drives, map to the LUN directly with the OS iSCSI initiator.

I haven't decided if we should place all our system drives on a single LUN or break them up into groups. I think I want to place domain controllers on their own LUN so I can restore our entire AD without the possibility of a USN rollback. And all our other servers don't really fall into groups... if start to think about splitting them up, it gets to the point where I might as well make a LUN for each of them. And from what I've read so far, performance isn't really a problem if you have less than 16 VMs on a LUN.

So with all the system drives (except AD) on a single LUN, restores become a little more complicated. Not too hard.. just harder than using individual LUNs. We would need to bring up a snapshot on a new LUN, mount the LUN on ESX server (or maybe somewhere else), and copy the VMDK of the machine we're restoring over to the production LUN.

If there is a LUN for each system drive, restoring from a snapshot would just require a click on the EqualLogic array's web interface, and everything would be back.

So what are we going to do? I still don't know yet. And there's plenty of time to decide, and neither way is the "wrong way" (nor the "right" way). So we'll see...