Comment 2 for bug 553737

From IRC from #ubuntu-server (excerpted):
09:36 < jdstrand> kirkland, smoser: in the past, libvirt created a new scsi
                  controller for every new device. this was a pci add which is
                  why it showed up magically
09:37 < jdstrand> kirkland, smoser: this is incorrect behavior and now libvirt
                  adds disks to an existing bus, like what would happen in the
                  real world
09:39 < jdstrand> smoser: also, aligouri (upstream qemu) reiterated that we
                  should not be using scsi hot add
09:47 < jdstrand> smoser: virtio hot add stills works
09:43 < smoser> it will absolutely break guests if devices don't "just show up"
09:48 < jdstrand> smoser: of course, kirkland mentioned euco is resistent to
                  vd* devices
10:05 < jdstrand> kirkland, smoser: so the decision comes down to: do we stick
                  with the old 0.7.5, lose the bug fixes but maintain
                  deprecated scsi behavior and not touch euca for an LTS, or
                  move to the new 0.7.7 with its fixes, but new scsi behavior
                  and updating euca
10:11 < smoser> the primary one, in my opinion, is that EBS (the functionality
                exposed by attach/detach) is supposed to promise that your data
                is SAFE
10:11 < smoser> and as we know, with buggy scsi, that is probably not the case.
10:13 < smoser> i'm open to a tested virtio solution because it is the
                "accepted solution" for hotplug
10:15 < jdstrand> I'm betting you will see a performance gain over scsi as well
10:15 < kirkland> jdstrand: oh, the performance gain is huge
10:16 < kirkland> jdstrand: we're going to insist on it [Ed. virtio] for lucid+1
10:20 < smoser> kirkland, jdstrand i think, for maintainability that this is
                probably somethign worth testing

So bottom line, for stability, integrity, maintainability and performance reasons, kirkland and smoser will test virtio attach and decide if it is worth pursuing. If so, 0.7.7 could still make it for Lucid.