Re: [Qemu-devel] [migration] questions about removing the old block-migration code

[Stefan Hajnoczi]

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