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Re: [Qemu-devel] [Qemu-block] [PATCH COLO v3 01/14] docs: block replicat
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [Qemu-block] [PATCH COLO v3 01/14] docs: block replication's description |
Date: |
Thu, 23 Apr 2015 10:55:09 +0100 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Wed, Apr 22, 2015 at 05:28:01PM +0800, Wen Congyang wrote:
> On 04/22/2015 05:18 PM, Stefan Hajnoczi wrote:
> > On Tue, Apr 21, 2015 at 05:28:01PM +0200, Paolo Bonzini wrote:
> >> On 21/04/2015 03:25, Wen Congyang wrote:
> >>>>> Please do not introduce "<name>+colo" block drivers. This approach is
> >>>>> invasive and makes block replication specific to only a few block
> >>>>> drivers, e.g. NBD or qcow2.
> >>> NBD is used to connect to secondary qemu, so it must be used. But the
> >>> primary
> >>> qemu uses quorum, so the primary disk can be any format.
> >>> The secondary disk is nbd target, and it can also be any format. The cache
> >>> disk(active disk/hidden disk) is an empty disk, and it is created before
> >>> run
> >>> COLO. The cache disk format is qcow2 now. In theory, it can be ant format
> >>> which
> >>> supports backing file. But the driver should be updated to support colo
> >>> mode.
> >>>
> >>>> A cleaner approach is a QMP command or -drive options that work for any
> >>>> BlockDriverState.
> >>>
> >>> OK, I will add a new drive option to avoid use "<name>+colo".
> >>
> >> Actually I liked the "foo+colo" names.
> >>
> >> These are just internal details of the implementations and the
> >> primary/secondary disks actually can be any format.
> >>
> >> Stefan, what was your worry with the +colo block drivers?
> >
> > Why does NBD need to know about COLO? It should be possible to use
> > iSCSI or other protocols too.
>
> Hmm, if you want to use iSCSI or other protocols, you should update the driver
> to implement block replication's control interface.
>
> Currently, we only support nbd now.
I took a quick look at the NBD patches in this series, it looks like
they are a hacky way to make quorum dynamically reconfigurable.
In other words, what you really need is a way to enable/disable a quorum
child or even add/remove children at run-time.
NBD is not the right place to implement that. Add APIs to quorum so
COLO code can use them.
Or maybe I'm misinterpreting the patches, I only took a quick look...
Stefan
pgpv_n7O0gNAK.pgp
Description: PGP signature
- [Qemu-devel] [PATCH COLO v3 00/14] Block replication for continuous checkpoints, Wen Congyang, 2015/04/03
- [Qemu-devel] [PATCH COLO v3 02/14] quorum: allow ignoring child errors, Wen Congyang, 2015/04/03
- [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's description, Wen Congyang, 2015/04/03
- Re: [Qemu-devel] [Qemu-block] [PATCH COLO v3 01/14] docs: block replication's description, Stefan Hajnoczi, 2015/04/20
- Re: [Qemu-devel] [Qemu-block] [PATCH COLO v3 01/14] docs: block replication's description, Wen Congyang, 2015/04/20
- Re: [Qemu-devel] [Qemu-block] [PATCH COLO v3 01/14] docs: block replication's description, Paolo Bonzini, 2015/04/21
- Re: [Qemu-devel] [Qemu-block] [PATCH COLO v3 01/14] docs: block replication's description, Stefan Hajnoczi, 2015/04/22
- Re: [Qemu-devel] [Qemu-block] [PATCH COLO v3 01/14] docs: block replication's description, Wen Congyang, 2015/04/22
- Re: [Qemu-devel] [Qemu-block] [PATCH COLO v3 01/14] docs: block replication's description,
Stefan Hajnoczi <=
- Re: [Qemu-devel] [Qemu-block] [PATCH COLO v3 01/14] docs: block replication's description, Wen Congyang, 2015/04/23
- Re: [Qemu-devel] [Qemu-block] [PATCH COLO v3 01/14] docs: block replication's description, Kevin Wolf, 2015/04/22
- Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's description, Paolo Bonzini, 2015/04/22
- Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's description, Kevin Wolf, 2015/04/23
- Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's description, Paolo Bonzini, 2015/04/23
- Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's description, Wen Congyang, 2015/04/23
- Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's description, Kevin Wolf, 2015/04/23
- Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's description, Wen Congyang, 2015/04/23
- Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's description, Paolo Bonzini, 2015/04/23
- Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's description, Kevin Wolf, 2015/04/23