Hyper-V Requirements, disk partitioning

If you don't plan on using the host OS to run anything but Hyper-V, I don't think putting VMs on the same partition as the OS is going to matter much. I'm using Hyper-V on a couple workstations with 10k rpm disks with the OS on one and VMs on both and I don't notice a difference in VM performance between them.

You can eat up disk very rapidly with VMs, so its worth having a big & slower disk for archives & backups (maybe not necessary if you have good network storage and a fast network).

If you are building it yourself and want to stay within a reasonable budget, I'd suggest 4-6x 10 rpm disks in raid 10 (300 GB disks can be had for ~$200 each on NewEgg). Then maybe 2x 1-2TB disks in raid 1 (if you add this, you might as well put the OS on it).

Using dynamically expanding disks and snapshots both adversely affect performance (for virtualizing a workstation it's fine, for a server maybe not). And for any disk intensive service, I'd use direct access to the service's backing store (e.g., database or file-server). If you move the I/O bottleneck off the virtual OS partition, you can probably snapshot the virtual server OS without worrying about performance.

Finally - you may want more than 8GB (Hyper-V can't share unallocated RAM, and the host needs some, too) - but that depends on how intensely they will be used.

I hope this is useful. And if you do some experimentation and benchmarking, I think many people would be interested to see the results. As you've probably noticed, there is a paucity of performance data in this area.

In a virtual Machine, the disk is the biggest bottleneck. When I build a VMHost, I use a 1TB drive with a 60 GB OS partition and use the rest to backup the VMs to. I then use 4 or 6 velociraptors in a raid 5 or 10. That gives them the speed that they WILL need as well as some redundancy.

Using raid 1 with 2 slow 2TB drives is just going to be a headache in the future. Again, the disk is the biggest bottleneck.

PS with the cost and overhead that Server 2008 brings, I have always used Server 2003 with Virtual Server 2005 and it has worked great.

Putting the OS on a separate physical disk(s) is definitely useful if you're running Hyper-V, because that actually runs on top of Windows, so the OS actually has some overhead (as opposed to, say, ESX/i, which has a really small footprint); a dedicated disk (or array) for OS and pagefile can really help.

Regarding VMs: what kind of workload will they have? Memory? CPU? Disk? If they work a lot with storage, then putting them on separate physical disk(s) will provide a real advantage; if they do very low disk I/O, you can put them all in the same place and there won't be any difference.

If you have two very disk-intensive VMs to run, I'd go with three RAID1 arrays, one (small) for the OS and pagefile and one (large enough) for each VM.