Hello, I'm looking at building a new system in shortly and am at a bit of a dilemma regarding storage. I'm curious to hear peoples real-world opinions/experience as unfortunately I neither have the budget nor the available hardware to test & benchmark this kind of thing myself :-(

Currently I have a system with 4x 1TB SATA HDDs in RAID-10 (effectively ~1TB usable) and allocate each VM two LVM volumes (one for the filesystem and one swap). I think this is a common setup in Xen circles which I have migrated from. Now I allocate each VM a nice chunk of storage space but the reality is only 25-30% space is used.. This leads me to wonder, should I consider 4x 300GB SAS drives in RAID-10 using QCOW2 sparse files instead? Will I gain a measurable performance from the faster disks vs the QCOW2 file overhead?

Does anyone have any decent benchmarks/articles on this subject, if so I'm all ears! Obviously my goal is to get the best disk performance per $ :-) VMs are typically light/medium-duty web/mail workloads etc.

Thanks for looking!