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From: Christian Theune <ct@gocept.com>
Date: Thu, 13 Sep 2012 16:58:23 +0200
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Subject: [Qemu-devel] Selective block migration (still on 0.13)
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To: qemu-devel@nongnu.org

Hi,

we're currently still on 0.13, looking forward to a large update soon. :)

We haven't been using live migration up until now, but are 
investigating it to multiple downtimes (restarting updated hosts and 
restarting updated guests) when doing system updates. So, we're trying 
to find out whether we can get this into a usable shape while still 
running 0.13.

I saw that 0.13 does have block migration available. However, looking 
at the code, it's an "either or" situation: migrate all block devices 
or none.

In our case we have the root disks on iSCSI (through virtio-blk) and 
two additional local disks (for /tmp and swp).

Now, the iSCSI shouldn't be migrated but the local disks should.

Reading up in the current code, it doesn't look like this would be 
feasable. Can someone prove me wrong? Please? :)

Even the earlier discussion regarding live block copy which included a 
reference to using libvirt sounds like it would have a problem 
instrumenting the live migration correctly: how do you get the 
migration atomic if you need to copy the block devices independent of 
the VM migration? Maybe, I'm missing something.

Cheers,
Christian