From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1G7bug-0006lt-Gk for qemu-devel@nongnu.org; Mon, 31 Jul 2006 13:50:46 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1G7bud-0006lh-0L for qemu-devel@nongnu.org; Mon, 31 Jul 2006 13:50:46 -0400 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1G7buc-0006le-Ts for qemu-devel@nongnu.org; Mon, 31 Jul 2006 13:50:42 -0400 Received: from [64.233.182.188] (helo=nf-out-0910.google.com) by monty-python.gnu.org with esmtp (Exim 4.52) id 1G7bxK-0000rR-TN for qemu-devel@nongnu.org; Mon, 31 Jul 2006 13:53:31 -0400 Received: by nf-out-0910.google.com with SMTP id a25so550946nfc for ; Mon, 31 Jul 2006 10:50:41 -0700 (PDT) Message-ID: Date: Mon, 31 Jul 2006 19:50:41 +0200 From: "andrzej zaborowski" Sender: balrogg@gmail.com Subject: Re: [Qemu-devel] [RFC][PATCH] make sure disk writes actually hit disk In-Reply-To: <20060731101710.GQ14748@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <44CA6B76.7000004@redhat.com> <44CB310B.9060308@bellard.org> <44CB77DF.9030700@redhat.com> <20060730214147.GA6255@mail.shareable.org> <20060731101710.GQ14748@suse.de> Reply-To: balrogg@gmail.com, qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jens Axboe Cc: qemu-devel@nongnu.org On 31/07/06, Jens Axboe wrote: > On Mon, Jul 31 2006, andrzej zaborowski wrote: > > On 30/07/06, Jamie Lokier wrote: > > >Rik van Riel wrote: > > >> This may look like hair splitting, but so far I've lost a > > >> (test) postgresql database to this 3 times already. Not getting > > >> the guest application's data to disk when the application calls > > >> fsync is a recipe for disaster. > > > > > >Exactly the same thing happens with real IDE disks if IDE write > > >caching (on the drive itself) is enabled, which it is by default. It > > >is rarer, but it happens. > > > > The little difference with QEMU is that there are two caches above it: > > the host OS'es software cache and the IDE hardware cache. When a guest > > OS flushes its own software cache its precious data goes to the host's > > software cache while the guest thinks it's already the IDE cache. This > > is ofcourse of less importance because data in both caches (hard- and > > software) is lost when the power is cut off. > > But the drive cache does not let the dirty data linger for as long as > wht OS page/buffer cache. I would say this an argument speaking for actually using O_SYNC. > > > IMHO what really makes IO unreliable in QEMU is that IO errors on the > > host are not reported to the guest by the IDE emulation and there's an > > exact place in hw/ide.c where they are arrogantly ignored. > > Send a patch, I'm pretty sure nobody would disagree :-) Here's what I proposed: http://lists.gnu.org/archive/html/qemu-devel/2005-12/msg00275.html but I'm afraid it's not correct :P > > -- > Jens Axboe > > -- balrog 2oo6 Dear Outlook users: Please remove me from your address books http://www.newsforge.com/article.pl?sid=03/08/21/143258