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Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 ima
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 images |
Date: |
Fri, 28 Jun 2019 17:09:11 +0200 |
User-agent: |
Mutt/1.11.3 (2019-02-01) |
Am 28.06.2019 um 17:02 hat Alberto Garcia geschrieben:
> On Fri 28 Jun 2019 04:57:08 PM CEST, Kevin Wolf wrote:
> > Am 28.06.2019 um 16:43 hat Alberto Garcia geschrieben:
> >> On Thu 27 Jun 2019 06:05:55 PM CEST, Denis Lunev wrote:
> >> > Please note, I am not talking now about your case with COW. Here the
> >> > allocation is performed on the sub-cluster basis, i.e. the abscence of
> >> > the sub-cluster in the image means hole on that offset. This is
> >> > important difference.
> >>
> >> I mentioned the possibility that if you have a case like 2MB / 64KB
> >> and you write to an empty cluster then you could allocate the
> >> necessary subclusters, and additionally fallocate() the space of the
> >> whole cluster (2MB) in order to try to keep it contiguous.
> >>
> >> With this we would lose the space saving advantage of having
> >> subclusters. But perhaps that would work for smaller cluster sizes
> >> (it would mitigate the fragmentation problem).
> >
> > There seem to be use cases for both ways. So does this need to be an
> > option?
>
> Probably a runtime option, or a heuristic that decides what to do
> depending on the cluster size.
How would the heuristic decide whether the user wants to save disk space
or whether they consider avoiding fragmentation (i.e. performance) more
important?
Kevin
- Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 images, (continued)
- Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 images, Denis Lunev, 2019/06/27
- Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 images, Alberto Garcia, 2019/06/28
- Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 images, Denis Lunev, 2019/06/28
- Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 images, Kevin Wolf, 2019/06/28
- Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 images, Alberto Garcia, 2019/06/28
- Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 images, Denis Lunev, 2019/06/28
- Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 images, Alberto Garcia, 2019/06/28
- Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 images, Kevin Wolf, 2019/06/28
- Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 images,
Kevin Wolf <=
- Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 images, Alberto Garcia, 2019/06/28
Re: [Qemu-block] [RFC] Re-evaluating subcluster allocation for qcow2 images, Kevin Wolf, 2019/06/27