To extend that question: While playing with that I've noticed linux
does not automagically find the a scsi disk hot-plugged in. After
reboot (and the scsi bus rescan triggered by that) it finds the
disk. Reloading the driver module probably would have worked too. We
don't signal the guest in any way it got a new disk, so this isn't
exactly surprising. Is this just a emulation limitation? Or a
limitation of the emulated scsi host adapters?
What appens when you hotplug or just switch on a real SCSI device? Does
Linux pick it up automatically? Long ago when I last tried that, I
think I had to do a magic write to sysfs to make it look for the device.