[libvirt] dynamic scsi disk attach seems to be broken in qemu(-kvm)-0.11, libvirt-0.7.1

[Dustin Kirkland]

On Fri, Oct 9, 2009 at 3:18 AM, Daniel P. Berrange <berrange at redhat.com> wrote:
> On Thu, Oct 08, 2009 at 10:57:55PM -0500, Dustin Kirkland wrote:
>> Now, all of that said, it is actually possible to hot-add a second
>> scsi device. However, as far as I can tell, this method is not yet
>> supported by libvirt.  It looks to me that with modern qemu, you have
>> to do it this way:
>>
>> Drop to a qemu console with ctrl-alt-2. Get the address of the current scsi bus:
>>   (qemu) info pci
>>   Look for "SCSI Controller". In my case, it's on Bus 0, device 4, function 0
>>
>> Now instead of pci_add, use drive_add
>>   (qemu) drive_add 0:4 file=/tmp/foo,if=scsi
>>   OK bus 0, unit 1
>
> That is correct - the SCSI driver hotplug in libvirt is not implemented
> in the right way. If you specify multiple SCSI devices at boot, they
> all get on one controller, if you hotplug multiple SCSI devices, we're
> hotplugging a new SCSI controller per disk. This is clearly not good,
> because when you then reboot, all those controllers are merged back into
> one.

Okay, in our previous usage of this, rebooting didn't matter very much.

> There is a guy who is working on implementing the correct SCSI hotplug
> approach for libvirt, that is still work in progress though. The most
> recent patches were here:
>
> http://www.redhat.com/archives/libvir-list/2009-September/msg00551.html
>
> We will ultimately support hotplug of both drives, and drive controllers
> independantly, giving apps/users the flexibility they need.

Thanks.  I'll track those patches with interest.

:-Dustin