From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?ISO-8859-1?Q?Jens_Kristian_S=F8gaard?= Subject: Re: [ceph-users] snapshot, clone and mount a VM-Image Date: Sun, 17 Feb 2013 00:16:40 +0100 Message-ID: <51201358.3010103@mermaidconsulting.dk> References: <5118C6BF.70207@risc-software.at> <5118FA0D.606@42on.com> <5118FB31.6020902@risc-software.at> <511D3A35.7090702@mermaidconsulting.dk> <511F72D2.5020104@mermaidconsulting.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mx03.stofanet.dk ([212.10.10.13]:57396 "EHLO mx03.stofanet.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754687Ab3BPXQo (ORCPT ); Sat, 16 Feb 2013 18:16:44 -0500 In-Reply-To: Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Sage Weil Cc: Wolfgang Hennerbichler , ceph-devel@vger.kernel.org Hi Sage, > Would qcow2 let you store the incremental portion of a backup without= the=20 > actual image? A common use case would be: > - take snapshot1 on cluster A > - copy image to cluster B, possibly without writing to an intermediat= e=20 > file.. e.g. 'rbd export ... - | ssh otherhost rbd import - ...' > and later, > - take snapshot2 on cluster A > - stream snapshot1->2 incremental to cluster B Well, qcow2 is designed for storing image files on disk, not as a=20 "streamed" file format - so it is not covered by the specification.=20 However, I don't see what should keep us from using it the way you desc= ribe. The only drawback is that standard qcow2 tools will not be able to work= =20 with the incremental file on its own - they would need the base image t= o=20 be file based. Basically a qcow2 "incremental" file contains: - string holding the path and filename of the backing file - lookup table that tells which blocks are included in the file - actual data in 512 byte blocks In this "streaming" case we would not have a path and file to the=20 backing file. Instead we could store something like=20 rbd:pool/imagename@snapname instead of a traditional path and file name= =2E --=20 Jens Kristian S=F8gaard, Mermaid Consulting ApS, jens@mermaidconsulting.dk, http://www.mermaidconsulting.com/ -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html