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Date: Fri, 10 Oct 2008 12:03:25 +0200
From: Fabrice Bellard <fabrice@bellard.org>
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Subject: Re: [Qemu-devel] [RFC] Disk integrity in QEMU
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To: qemu-devel@nongnu.org
Cc: Chris Wright <chrisw@redhat.com>, Mark McLoughlin <markmc@redhat.com>, Ryan Harper <ryanh@us.ibm.com>, Laurent Vivier <Laurent.Vivier@bull.net>, kvm-devel <kvm-devel@lists.sourceforge.net>

Anthony Liguori wrote:
> [...]
> So to summarize, I think we should enable O_DSYNC by default to ensure
> that guest data integrity is not dependent on the host OS, and that
> practically speaking, cache=off is only useful for very specialized
> circumstances.  Part of the patch I'll follow up with includes changes
> to the man page to document all of this for users.
> 
> Thoughts?

QEMU is also used for debugging and arbitrary machine simulation. In
this case, using uncached accesses is bad because you want maximum
isolation between the guest and the host. For example, if the guest is a
development OS not using a disk cache, I still want to use the host disk
cache.

So the "normal" caching scheme must be left as it is now. However, I
agree that the default behavior could be modified.

Regards,

Fabrice.