On Thu, Jun 07, 2018 at 01:19:29PM +0300, Vladimir Sementsov-Ogievskiy wrote: > 07.06.2018 13:10, Stefan Hajnoczi wrote: > > On Fri, Jun 01, 2018 at 07:16:14PM +0300, Vladimir Sementsov-Ogievskiy > > wrote: > > > 20.02.2017 17:59, Peter Lieven wrote: > > > > Am 20.02.2017 um 15:50 schrieb Stefan Hajnoczi: > > > > > On Fri, Feb 17, 2017 at 05:00:24PM +0100, Peter Lieven wrote: > > > > > > this is something I have been thinking about for almost 2 years now. > > > > > > we heavily have the following two use cases when using qemu-img > > > > > > convert. > > > > > > > > > > > > > > > [...] > > > > > > > > Does this patch work with compressed images? Especially the > > > > > out-of-order write mode may be problematic with a compressed qcow2 > > > > > image. > > > > It does, but you are right, out-of-order writes and compression should > > > > be mutually exclusive. > > > > > > Sorry for being late, but can you please explain to me, why? > > There are image format-specific limitations on compressed writes. For > > some reason I thought they were append-only in qcow2, but I was wrong. > > > > Stefan > > And what are limitations for compressed writes in qcow2?
Writes must be cluster-aligned and the size must be 1 cluster (except for the last cluster in an image). qemu-img convert honors this, so it's not a problem. > We can't write asynchronously? Why? Async compressed writes are supported nowadays. I think my original comment was wrong. It should be fine to use out-of-order compressed writes. Stefan
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