From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1Kp9v5-0000Cz-Py
	for qemu-devel@nongnu.org; Sun, 12 Oct 2008 19:00:15 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1Kp9v3-0000CV-IP
	for qemu-devel@nongnu.org; Sun, 12 Oct 2008 19:00:15 -0400
Received: from [199.232.76.173] (port=50228 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1Kp9v3-0000CR-E8
	for qemu-devel@nongnu.org; Sun, 12 Oct 2008 19:00:13 -0400
Received: from mail2.shareable.org ([80.68.89.115]:34337)
	by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32)
	(Exim 4.60) (envelope-from <jamie@shareable.org>) id 1Kp9v3-0001h7-Cj
	for qemu-devel@nongnu.org; Sun, 12 Oct 2008 19:00:13 -0400
Date: Mon, 13 Oct 2008 00:00:07 +0100
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] [RFC] Disk integrity in QEMU
Message-ID: <20081012230006.GA22509@shareable.org>
References: <48EE38B9.2050106@codemonkey.ws> <48EF0A26.90209@redhat.com>
	<48EF2120.7070606@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <48EF2120.7070606@redhat.com>
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
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>

Avi Kivity wrote:
> The IDE write cache is not susceptible to software failures (well it is 
> susceptible to firmware failures, but let's ignore that).  It is likely 
> to survive reset and perhaps even powerdown.  The risk window is a few 
> megabytes and tens of milliseconds long.

Nonetheless, from yanking the power relatively often while using ext3
(this is on a host only, no qemu involved) I've seen a number of
corruption cases, and these all went away when the IDE write cache was
disabled, or when IDE write barriers were used.

This is a failure case which happens in real life, but not often if
you don't often yank the power during writes.

Just so you know.

-- Jamie