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Date: Tue, 21 Apr 2015 17:28:01 +0200
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Subject: Re: [Qemu-devel] [Qemu-block] [PATCH COLO v3 01/14] docs: block
 replication's description
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To: Wen Congyang <wency@cn.fujitsu.com>, Stefan Hajnoczi <stefanha@gmail.com>
Cc: Fam Zheng <famz@redhat.com>, Lai Jiangshan <laijs@cn.fujitsu.com>, qemu block <qemu-block@nongnu.org>, Jiang Yunhong <yunhong.jiang@intel.com>, Dong Eddie <eddie.dong@intel.com>, qemu devel <qemu-devel@nongnu.org>, Max Reitz <mreitz@redhat.com>, Gonglei <arei.gonglei@huawei.com>, Stefan Hajnoczi <stefanha@redhat.com>, Yang Hongyang <yanghy@cn.fujitsu.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, zhanghailiang <zhang.zhanghailiang@huawei.com>



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?

Paolo