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Date: Fri, 22 Aug 2014 15:13:31 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v12 0/6] qcow2,
 raw: add preallocation=full and preallocation=falloc
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To: "Richard W.M. Jones" <rjones@redhat.com>
Cc: Hu Tao <hutao@cn.fujitsu.com>, Max Reitz <mreitz@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, Yasunori Goto <y-goto@jp.fujitsu.com>

Am 22.08.2014 um 14:25 hat Richard W.M. Jones geschrieben:
> 
> On Mon, Jul 28, 2014 at 04:48:46PM +0800, Hu Tao wrote:
> > ping...
> > 
> > All the 6 patches have reviewed-by now.
> > 
> > On Fri, Jul 11, 2014 at 02:09:57PM +0800, Hu Tao wrote:
> > > This series adds two preallocation mode to qcow2 and raw:
> > > 
> > > Option preallocation=full preallocates disk space for image by writing
> > > zeros to disk, this ensures disk space in any cases.
> > > 
> > > Option preallocation=falloc preallocates disk space by calling
> > > posix_fallocate(). This is faster than preallocation=full.
> 
> Sorry if this was discussed before, but why would anyone use
> preallocation=full if preallocation=falloc was possible?
> 
> Shouldn't preallocation=full simply use posix_fallocate if it's
> available, and fall back to writing zeroes if not?

posix_fallocate() is basically metadata preallocation on the file
system level. If any lower levels involve allocations as well, does
posix_fallocate() allocate them there?

Kevin