I have a couple of KVM nodes with 4xSATA drives in RAID10, which I am using as a VPS node. I have a LVM set up, and I am using SolusVM for the nodes. There's already 30 VPSes each on the nodes, so I can not reformat the node, rebooting it is going to be emotionally hurtful, and I can not format individual VPSes.
I've read about QCOW somewhere, well, only saw it mentioned somewhere, and heard it could be used to thin provision the disk on KVM nodes. Can I convert the currently provisioned VPSes to QCOW without having to format them? Or does it require changes to the hosts filesystem/partition table? How about any new VPSes I add? I don't think SolusVM has an option for this built-in. Or does it? If it does, I might have missed it. So how do you thin provision a disk in KVM?

Anyone?

1. you can use LVs with qcow2 format, but the LVs will not autoexpand without some subsystem monitoring them and running lvextend when the LV nears it's capacity. Thin provisioned LVs exist in the latest RHEL versions, but I haven't tried those with KVM yet.
2. to move to a FS based set of qcow2 images is simple enough - run qemu-img convert from the existing LV to a file, and you're done. Will require downtime of course.
3. No idea what solus supports, but if you use RHEV or oVirt, they have thin provisioning based on LVM working quite well, with no additional configuration required at all.