On Tue, 03 Dec 2013 18:13:08 +0100 Oliver Brakmann <oliver.brakmann@posteo.de> wrote:
Hello,
On 2013-11-22 21:46, Michael Mol wrote:
I know that lvm supports thin provisioning, and I think I have a pretty good grasp on how that works. Does libvirt support lvm thin provisioning and thin snapshots?
libvirt does not support storage pools containing thin pools. Since commit 4132dede0652b7f0cc83868fd454423310bc1a9c (http://libvirt.org/git/?p=libvirt.git;a=commit;h=4132dede0652b7f0cc83868fd45...) at least the thick provisioned volumes in such a pool can still be used. Previously, libvirt would just refuse to start the pool.
However, you can assign any thin provisioned volume to a VM manually and it will work. On the hardware/software combination that I tried it on (desktop SATA drives in RAID1 on Ubuntu 13.10) it was abysmally slow though.
I would expect that. My setup would be: RAID6 | PV | VG | thin pool Where the RAID6 is provided by a hardware RAID controller with a battery-backed write cache.
Proper support for LVM thin provisioning would probably need a new storage pool type, and I haven't found any hints that anybody was working on that.
A pity. Thin provisioning would be (as I see it) the first step to whole-VM snapshots as found in systems like VMWare ESX. I'd love to be able to pull that off using Linux/QEMU/KVM. Or at least be able to snapshot a running VM's disk to be able to pull backups off the snapshot without interrupting service in the VM guests.