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