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Date: Sun, 12 Oct 2008 13:02:57 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [RFC] Disk integrity in QEMU
References: <48EE38B9.2050106@codemonkey.ws>	<48EF1D55.7060307@redhat.com>	<48F0E83E.2000907@redhat.com>	<48F10DFD.40505@codemonkey.ws>	<20081012004401.GA9763@acer.localdomain>
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To: Dor Laor <dor.laor@qumranet.com>
Cc: Chris Wright <chrisw@redhat.com>, Mark McLoughlin <markmc@redhat.com>, kvm-devel <kvm@vger.kernel.org>, Laurent Vivier <Laurent.Vivier@bull.net>, qemu-devel@nongnu.org, Ryan Harper <ryanh@us.ibm.com>

Dor Laor wrote:
> Avi Kivity wrote:
>
> Since there is ongoing effort (both by IT and developers) to keep the 
> base images as big as possible, it guarantees that
> this data is best suited for caching in the host while the private 
> leaf images will be uncached.

A proper CAS solution is really such a better approach.  qcow2 
deduplification is an interesting concept, but such a hack :-)

> This way we provide good performance and caching for the shared parent 
> images while also promising correctness.

You get correctness by using O_DSYNC.  cache=off should disable the use 
of the page cache everywhere.

Regards,

Anthony Liguori

> Actually this is what happens on mainline qemu with cache=off.
>
> Cheers,
> Dor
> -- 
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