From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1KpRi5-00031M-5y for qemu-devel@nongnu.org; Mon, 13 Oct 2008 14:00:01 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1KpRi4-00030w-Dr for qemu-devel@nongnu.org; Mon, 13 Oct 2008 14:00:00 -0400 Received: from [199.232.76.173] (port=45827 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1KpRi4-00030p-9b for qemu-devel@nongnu.org; Mon, 13 Oct 2008 14:00:00 -0400 Received: from mx2.redhat.com ([66.187.237.31]:57986) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1KpRi2-00087Q-B7 for qemu-devel@nongnu.org; Mon, 13 Oct 2008 14:00:00 -0400 Message-ID: <48F38C5E.1080504@redhat.com> Date: Mon, 13 Oct 2008 13:58:54 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [Qemu-devel] [RFC] Disk integrity in QEMU References: <48EE38B9.2050106@codemonkey.ws> In-Reply-To: <48EE38B9.2050106@codemonkey.ws> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Chris Wright , Mark McLoughlin , Ryan Harper , Laurent Vivier , kvm-devel Anthony Liguori wrote: > When cache=on, read requests may not actually go to the disk. If a > previous read request (by some application on the system) has read the > same data, then it becomes a simple memcpy(). Also, the host IO > scheduler may do read ahead which means that the data may be available > from that. This can be as much of a data integrity problem as asynchronous writes, if various qemu/kvm guests are accessing the same disk image with a cluster filesystem like GFS. -- All rights reversed.