I don't have physical access to the machine, so I can't unplug the drive.
# hdparm -I /dev/sda | grep frozen frozen
The advice I've read elsewhere is to hotplug the drive, pull the power / sata cables while the machine is running. Those are not possible in this situation as I don't have physical access. I've tried power cycling the machine through the host's control panel a few times, but that hasn't worked.
Is there any way I can unfreeze (unfrozen?) the drive without physical access?