libvirt users - Nov 2018 - Re: lvm vs qcow (on NVMe)

hi guys,

anybody observed, maybe has measured performance difference between the 
two with qemu quests(windows OS)?

Any conclusions, recommendations?

many thanks, L.

On Fri, Oct 26, 2018 at 12:32:48PM +0100, lejeczek
wrote:
> hi guys,
> 
> anybody observed, maybe has measured performance difference between
> the two with qemu quests(windows OS)?
> 
> Any conclusions, recommendations?
[Cc Stefan from QEMU, probably he might have some pointers.]

-- 
/kashyap

On Thu, Nov 22, 2018 at 05:03:43PM +0100, Kashyap Chamarthy
wrote:
> On Fri, Oct 26, 2018 at 12:32:48PM +0100, lejeczek wrote:
> > hi guys,
> > 
> > anybody observed, maybe has measured performance difference between
> > the two with qemu quests(windows OS)?
> > 
> > Any conclusions, recommendations?
> 
> [Cc Stefan from QEMU, probably he might have some pointers.]
You can get good performance with qcow2 if you preallocate the image
file:

  $ qemu-img create -f qcow2 -o preallocation=falloc vm001.qcow2 10G

Writing to new regions of the image has a higher cost without
preallocation.  The downside is that the storage will be reserved for
the disk image so you no longer start off with a tiny file that grows on
demand.  That's the trade-off if performance is critical.

Stefan