From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1LYSzz-0002Tx-3B for qemu-devel@nongnu.org; Sat, 14 Feb 2009 17:28:35 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1LYSzx-0002TI-F9 for qemu-devel@nongnu.org; Sat, 14 Feb 2009 17:28:34 -0500 Received: from [199.232.76.173] (port=37341 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LYSzx-0002TD-7y for qemu-devel@nongnu.org; Sat, 14 Feb 2009 17:28:33 -0500 Received: from mx2.redhat.com ([66.187.237.31]:58015) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1LYSzw-0004SH-Kj for qemu-devel@nongnu.org; Sat, 14 Feb 2009 17:28:33 -0500 Message-ID: <499745A1.3040707@redhat.com> Date: Sun, 15 Feb 2009 00:28:49 +0200 From: Dor Laor MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: qcow2 corruption observed, fixed by reverting old change References: <20090211070049.GA27821@shareable.org> <49955681.9070301@suse.de> <20090213162336.GI18471@shareable.org> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Reply-To: dlaor@redhat.com, qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Marc Bevand Cc: qemu-devel@nongnu.org, Gleb Natapov , kvm@vger.kernel.org Marc Bevand wrote: > On Fri, Feb 13, 2009 at 8:23 AM, Jamie Lokier wrote: > >> Marc.. this is quite a serious bug you've reported. Is there a >> reason you didn't report it earlier? >> > > Because I only started hitting that bug a couple weeks ago after > having upgraded to a buggy kvm version. > > >> Is there a way to restructure the code and/or how it works so it's >> more clearly correct? >> > > I am seriously concerned about the general design of qcow2. The code > base is more complex than it needs to be, the format itself is > susceptible to race conditions causing cluster leaks when updating > some internal datastructures, it gets easily fragmented, etc. > > I am considering implementing a new disk image format that supports > base images, snapshots (of the guest state), clones (of the disk > content); that has a radically simpler design & code base; that is > always consistent "on disk"; that is friendly to delta diffing (ie. > space-efficient when used with ZFS snapshots or rsync); and that makes > use of checksumming & replication to detect & fix corruption of > critical data structures (ideally this should be implemented by the > filesystem, unfortunately ZFS is not available everywhere :D). > > I believe the key to achieve these (seemingly utopian) goals is to > represent a disk "image" as a set of sparse files, 1 per > snapshot/clone. > Both qcow2 and vmdk have the ability to keep 'external' snapshots. In addition to what you wrote, qcow2 is missing journal for its meta data and also performs poorly because of complex meta data and sync calls. We might use vmdk format or VHD as a base for the future high performing, safe image format for qemu -dor > -marc > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >