From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH][RFC] Use writeback caching by default with qcow2 Date: Thu, 20 Nov 2008 11:55:15 +0200 Message-ID: <49253403.6060603@redhat.com> References: <49247615.6050105@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, qemu-devel@nongnu.org To: Thomas Mueller Return-path: Received: from mx2.redhat.com ([66.187.237.31]:58336 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753347AbYKTJzV (ORCPT ); Thu, 20 Nov 2008 04:55:21 -0500 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: Thomas Mueller wrote: >> Right now, qcow2 isn't a >> reliable format regardless of the type of cache your using because >> metadata is not updated in the correct order. >> > > so you don't advise to use qcow2 as a VBD or what do you mean with "isn't > reliable"? > Right, qcow2 is both very slow with cache=writethrough (or off), and may corrupt itself if the host crashes at the wrong moment. > or contrawise: on the other formats the metadata is updated in the > correct order? > raw is the only format we're sure of. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.