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Re: [Qemu-devel] [RFC] Proposed qcow2 extension: subcluster allocation

From: Kevin Wolf
Subject: Re: [Qemu-devel] [RFC] Proposed qcow2 extension: subcluster allocation
Date: Mon, 10 Apr 2017 10:42:50 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 07.04.2017 um 19:10 hat Max Reitz geschrieben:
> One case I'd be especially interested in are of course 4 kB subclusters
> for 64 kB clusters (because 4 kB is a usual page size and can be
> configured to be the block size of a guest device; and because 64 kB
> simply is the standard cluster size of qcow2 images nowadays[1]...).

Why should the current default cluster size be an argument for anything?
64k is a tradeoff between small COW size and large allocation
granularity that seemed to work well (and it used to be the maximum
cluster size originally, so it seemed safer than 128k).

With subclusters, we have a completely different situation and need to
find a new default that works best. I'm relatively sure that 64k are too
small under the new conditions.

Also, undefined reference: [1] (I was hoping to find a better argument


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