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Re: [Qemu-devel] Fw:Re:What does "COW" mean?
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From: |
Stefan Hajnoczi |
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Subject: |
Re: [Qemu-devel] Fw:Re:What does "COW" mean? |
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Date: |
Wed, 3 Sep 2014 12:01:42 +0100 |
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User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Wed, Sep 03, 2014 at 12:47:44PM +0800, shhuiw wrote:
> At 2014-09-02 04:33:50, "shhuiw" <address@hidden> wrote:
> >
> >
> >Hi,
> >
> >I'm new to qemu community, and I'm trying the COW image format (old but
> >simple:-).
> >I have read through its source code, and didn't find anything about 'copy on
> >write'.
> >I wonder wthat "COW" stands for?
>
> Sorry for my unclear expression.
> I mean when copy-on-write happens if COW image format is used, and how the
> COW driver code handles cop-on-write?
It doesn't really "copy on write" but it is a sparse overlay. Only
written sectors need to be allocated in the image file, other sectors
will be read from the backing file.
Stefan
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