From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=54212 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OBpOL-0000vI-VL for qemu-devel@nongnu.org; Tue, 11 May 2010 09:21:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OBpOK-0003Ak-64 for qemu-devel@nongnu.org; Tue, 11 May 2010 09:20:57 -0400 Received: from mail-gy0-f173.google.com ([209.85.160.173]:64706) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OBpOK-0003Aa-3G for qemu-devel@nongnu.org; Tue, 11 May 2010 09:20:56 -0400 Received: by gyd5 with SMTP id 5so2602607gyd.4 for ; Tue, 11 May 2010 06:20:55 -0700 (PDT) Message-ID: <4BE959B2.3090904@codemonkey.ws> Date: Tue, 11 May 2010 08:20:50 -0500 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [PATCH 2/2] Add flush=off parameter to -drive References: <1273528310-7051-1-git-send-email-agraf@suse.de> <201005111315.08897.paul@codesourcery.com> <4BE950E0.5050107@codemonkey.ws> <201005111412.02809.paul@codesourcery.com> In-Reply-To: <201005111412.02809.paul@codesourcery.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paul Brook Cc: Kevin Wolf , Alexander Graf , armbru@redhat.com, qemu-devel@nongnu.org, Christoph Hellwig On 05/11/2010 08:12 AM, Paul Brook wrote: >>> cache=always (or a more scary name like cache=lie to defend against >>> idiots) >>> >>> Reads and writes are cached. Guest flushes are ignored. Useful for >>> dumb guests in non-critical environments. >>> >> I really don't believe that we should support a cache=lie. There are >> many other obtain the same results. For instance, mount your guest >> filesystem with barrier=0. >> > Ideally yes. However in practice I suspect this is still a useful option. Is > it even possible to disable barriers in all cases (e.g. NTFS under windows)? > > In a production environment it's probably not so useful - you're generally > dealing with long lived, custom configured guests. > > In a development environment the rules can be a bit different. For example if > you're testing an OS installer then you really don't want to be passing magic > mount options. If the host machine dies then you don't care about the state of > the guest because you're going to start from scratch anyway. > Then create a mount point on your host and mount the host file system under that mount with barrier=0. The problem with options added for developers is that those options are very often accidentally used for production. Regards, Anthony Liguori > Paul > >