From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=44227 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PsH0P-00076L-6B for qemu-devel@nongnu.org; Wed, 23 Feb 2011 10:51:58 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PsH0O-0005Wa-5V for qemu-devel@nongnu.org; Wed, 23 Feb 2011 10:51:57 -0500 Received: from mail-vw0-f45.google.com ([209.85.212.45]:48278) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PsH0O-0005WU-1y for qemu-devel@nongnu.org; Wed, 23 Feb 2011 10:51:56 -0500 Received: by vws19 with SMTP id 19so3896215vws.4 for ; Wed, 23 Feb 2011 07:51:55 -0800 (PST) Message-ID: <4D652D22.9080605@codemonkey.ws> Date: Wed, 23 Feb 2011 09:52:02 -0600 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: Strategic decision: COW format References: <4D5BC467.4070804@redhat.com> <4D5E4271.80501@redhat.com> <4D5E8031.5020402@codemonkey.ws> <4D637A20.9020307@redhat.com> <4D650F10.3060900@redhat.com> <4D651858.9040106@codemonkey.ws> <4D652675.1070908@redhat.com> <4D652868.8030908@codemonkey.ws> <4D6529A9.3090509@redhat.com> In-Reply-To: <4D6529A9.3090509@redhat.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: Avi Kivity Cc: Kevin Wolf , Chunqiang Tang , qemu-devel@nongnu.org, Stefan Hajnoczi , Markus Armbruster On 02/23/2011 09:37 AM, Avi Kivity wrote: > On 02/23/2011 05:31 PM, Anthony Liguori wrote: >>> >>>> what about snapshots? Are we okay having a feature in a prominent >>>> format that isn't going to meet user's expectations? >>>> >>>> Is there any hope that an image with 1000, 1000, or 10000 snapshots >>>> is going to have even reasonable performance in qcow2? >>>> >>> >>> Are thousands of snapshots for a single image a reasonable user >>> expectation? What's the use case? >> >> >> Checkpointing. It was the original use-case that led to qcow2 being >> invented. > > I still don't see. What would you do with thousands of checkpoints? Er, hit send to quickly. HPC is a big space where checkpointing is actually useful. An HPC workload may take weeks to run to completion. If something fails during the run, it's a huge waste of time. However, if you do regularl checkpointing, a failure may only lose a few minutes of work instead of the entire weeks worth of work. Regards, Anthony Liguori