What format to use for KVM Windows guests - RAW, QCOW2, VMDK

Hi everybody,

I was asking myself what would be the optimal format to chose for performance when using windows guests and KVM.
I have a 72GB SAS RAID-1 partition form ProxmoxVE3.0 and 500GB SATA RAID-1 mounted into a directory.

My intention is to do snapshots on the VMs and do backups to a fileserver automatically every week. I have maintenance windows so no need for live migration.

At the moment I am using qcow2 format and in the few tests I did it looks like I could do snapshots and backups with this format. So when reading in the wiki I found out that there may be performance leaks when using qcow2 and Microsoft SQL database. The wiki says to modify the SQL start parameter what I did and it says - better using RAW instead of qcow2.

So my questions are:
- Could I use RAW instead of qcow2 in my environment with my needs?
- Converting the VMs from qcow2 to RAW will probably work without problems using "qemu-img convert" command, right?
- Any other suggestion using the one format and not the other?
- I have some old WMDK VMs I need to use with proxmox. From performance view - any need to convert them from VMDK to qcow2 or VMDK to RAW?

Huh, more questions than I though ;)

Thank you!