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Re: [Qemu-devel] [RFC][PATCH] make sure disk writes actually hit disk


From: Jamie Lokier
Subject: Re: [Qemu-devel] [RFC][PATCH] make sure disk writes actually hit disk
Date: Sun, 30 Jul 2006 22:47:12 +0100
User-agent: Mutt/1.4.1i

Bill C. Riemers wrote:
>    How  about  compromising,  and  making  the  patch  a run time option.
>    Presumably  this  is  only  a  problem when the virtual machine is not
>    properly  shutdown.   For  those ho want the extra security of knowing
>    the  data  will  be written regardless of the shutdown status they can
>    enable  the  flag.  By default it could be turned off.  Then everybody
>    can be happy.

Real disks don't provide that security unless you disable the disk's
cache, or issue cache flush instructions to the disk.

Modern guest OS filesystems are written with this in mind.

With older guest OSes, you have to disable the disk cache if you want
that kind of security with real disks.

Is there any reason why the emulation should be any different?

-- Jamie




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