From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:58034) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Rv7N1-0003ks-JM for qemu-devel@nongnu.org; Wed, 08 Feb 2012 08:15:42 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Rv7Mq-00051k-JA for qemu-devel@nongnu.org; Wed, 08 Feb 2012 08:15:35 -0500 Received: from mx1.redhat.com ([209.132.183.28]:36335) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Rv7Mq-000516-CC for qemu-devel@nongnu.org; Wed, 08 Feb 2012 08:15:24 -0500 Message-ID: <4F326E99.7030904@redhat.com> Date: Wed, 08 Feb 2012 13:46:17 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <73865e0ce364c40e0eb65ec6b22b819d@mail.gmail.com> <4F31153E.9010205@codemonkey.ws> <4F311839.9030709@redhat.com> <4F311BBA.8000708@codemonkey.ws> <4F312FD3.5020206@zerto.com> <4F3137DB.1040503@redhat.com> <4F3139CE.4040103@zerto.com> <4F314798.8010009@redhat.com> <4F3211D0.3070502@zerto.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC PATCH] replication agent module List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Kevin Wolf , =?UTF-8?B?16rXldee16gg15HXnyDXkNeV16g=?= , =?UTF-8?B?16LXldeT15Mg16fXk9ed?= , dlaor@redhat.com, qemu-devel@nongnu.org, Ori Mamluk , Yair Kuszpet On 02/08/2012 01:03 PM, Stefan Hajnoczi wrote: > If you intend to run an unmodified drbd server on the rephub, then it > may not be possible to get point-in-time backups. (Although this > probably depends since things like btrfs or zfs may allow you to get > back to arbitrary transactions or timestamps.) I'm not sure what's the overhead, but btrfs copy-on-write (reflinks) may help. > But you could consider drbd as a network protocol and implement your > own server which speaks the protocol. Then you can add any > functionality you like, just like the case with the proprietary rephub > server you mentioned in your patch. > > So the only difference is that instead of using a new custom protocol > the rephub would need to speak the drbd protocol. So you're suggesting DRBD-over-NBD on the client, and for the replication hub a custom server speaking the DRBD protocol? I didn't find any documentation for DRBD and the code is only in the kernel, so this sounds like a lot of work. What about taking the existing Ceph/RBD driver in QEMU and changing it to support arbitrary image formats rather than just raw? That sounds much much easier. The main advantage is that Ceph has a user-space library for use in the replication hub. It also supports snapshots. Paolo