On Wed, Sep 03, 2014 at 12:47:44PM +0800, shhuiw wrote: > At 2014-09-02 04:33:50, "shhuiw" <shh...@163.com> 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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