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Date: Fri, 15 Nov 2013 16:33:46 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
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Subject: Re: [Qemu-devel] [migration] questions about removing the old
 block-migration code
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To: "Zhanghaoyu (A)" <haoyu.zhang@huawei.com>
Cc: "Huangweidong (C)" <weidong.huang@huawei.com>, "quintela@redhat.com" <quintela@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, Michal Privoznik <mprivozn@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, "paolo.bonzini@gmail.com" <paolo.bonzini@gmail.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Xiahai <xiahai@huawei.com>, Linqiangmin <linqiangmin@huawei.com>, Zanghongyong <zanghongyong@huawei.com>, Luonengjun <luonengjun@huawei.com>, "Huangpeng (Peter)" <peter.huangpeng@huawei.com>

On Fri, Nov 08, 2013 at 01:17:17AM +0000, Zhanghaoyu (A) wrote:
> >> I read below words on the report of <KVM Live Migration: Weather 
> >> forecast (May 29, 2013)>, We were going to remove the old 
> >> block-migration code Then people fixed it
> >> Good: it works now
> >> Bad: We have to maintain both
> >> It uses the same port than migration
> >> You need to migrate all/none of block devices
> >> 
> >> The old block-migration code said above is that in block-migration.c?
> >
> >Yes.
> >
> >> What are the reasons of removing the old block-migration code? Buggy implementation? Or need to migrate all/none of block devices?
> >
> >Buggy and tightly coupled with the live migration code, making it hard to modify either area independently.
> 
> Thanks a lot for explaining.
> Till now, we still use the old block-migration code in our virtualization solution.
> Could you detail the bugs that the old block-migration code have?

Please use git log block-migration.c to see bugs that have been fixed.

The basic problem is that block-migration.c hasn't been actively
maintained or used much.  My impression is that the newer block
migration approach using drive-mirror now has more developer and testing
focus (see libvirt if you're curious how drive-mirror can be
orchestrated).

Stefan