From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:46583) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RumWz-0005E5-6e for qemu-devel@nongnu.org; Tue, 07 Feb 2012 10:00:36 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RumWt-0001Ko-5t for qemu-devel@nongnu.org; Tue, 07 Feb 2012 10:00:28 -0500 Received: from mail-pw0-f45.google.com ([209.85.160.45]:34438) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RumWs-0001KM-J6 for qemu-devel@nongnu.org; Tue, 07 Feb 2012 10:00:23 -0500 Received: by pbaa11 with SMTP id a11so7981356pba.4 for ; Tue, 07 Feb 2012 07:00:21 -0800 (PST) Message-ID: <4F313C7C.3060201@codemonkey.ws> Date: Tue, 07 Feb 2012 09:00:12 -0600 From: Anthony Liguori 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> In-Reply-To: <4F3137DB.1040503@redhat.com> 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: Paolo Bonzini Cc: Kevin Wolf , dlaor@redhat.com, =?UTF-8?B?16LXldeT15Mg16fXk9ed?= , =?UTF-8?B?16rXldee16gg15HXnyDXkNeV16g=?= , qemu-devel@nongnu.org, Ori Mamluk On 02/07/2012 08:40 AM, Paolo Bonzini wrote: > On 02/07/2012 03:06 PM, Ori Mamluk wrote: >> The main issue about it is that the Rephub also needs the other >> direction - to read the protected volume. I get the feeling that with >> live block copy and NBD there's probably something that might fit >> this need, no? > > Yes, with two NBD sockets you could do it. But would you use both at the same > time? I would have thought that either the rephub is streaming from the > protected volume, or QEMU is streaming to the rephub. > > The current streaming code in QEMU only deals with the former. Streaming to a > remote server would not be supported. > >> With a 'new' agent like I need this is relatively easily achieved by a >> bidirectional protocol, but I agree a more generic protocol would be >> more elegant, although it will probably require a socket per direction, no? >> >> I Some smaller questions: >> * Is there already a working iScsi initiator as a block driver (I hope >> I'm using the right terminology) in Qemu, or do I need to write one? > > Yes, there is one using libiscsi. But I think Anthony was not referring to iSCSI > in particular, NBD would work just as well. > >> * This driver would need to be added in run-time - to allow starting to >> protect a running VM. Maybe via a monitor command. I guess that's OK, >> right? > > Yes, I think you can detach a block device from a drive and reattach the new > mirroring device. > >> * What can you say about NBD via iScsi - with respect to our >> requirements- who is more mature in Qemu? > > Personally I prefer NBD because it is lighter-weight and there is a server > inside QEMU (so you can use it easily with non-raw images). It is more mature, > but it is a bit less extensible. Which is also fine. You could also just use DRBD ;-) Regards, Anthony Liguori