in terms of migrating, it is essentially a relatively easy thing to do when power is all OFF and unpugged, and there is a page available here with more information about the migrations process, including a table to show which models can migrate to which models:
(when one of my drobo-s-gen2 models had a power toggle switch problem, i was able to successfully migrate my disk pack to another replacement drobo-s-gen2, and all was ok)[hr]
for the unmounting issue you are experiencing currently, can i check if you are having that, at random times, or even in the middle of doing things? or is it usually only after longer periods of inactivity, or possibly the mac sleeping?
it could be worth trying to use another connection cable, or to alternate from usb to firewire (or vice versa) just to see if that makes a difference, in case it is a faulty cable somehow?
my gen2 (touch wood) is still going strong, via usb, and the only time i ever had a corrupt file, was when it was the fault of a memory card on a camera (the source) which caused the image to have problems, and not the actual drobo, but yes, sometimes the operating system can affect things, though some disk maintenance utilts can help on a das drobo, like checkdisk for windows, and if you have diskwarrior, that has been known to fix a lot of issues on macs, that even the mac utils like diskutility have not been able to fix, and might help you too?