Can you specify the model of the Drobo? I don’t really recognize the model DRDSW2-A. Is it maybe a DroboFS (DRDS2-A)?
If it is a DroboFS, I was at one point able to reset a lost password on this model, but it involved a pinhole reset that was very poorly documented (or changed via firmware update, after the documentation was written). I believe this was the procedure I followed:
If you need the serial number, it should be printed on the bottom of the unit:
If only one drive out of 3 has failed, you should be able to see the entire contents of the Drobo as you have one drive fault tolerance. There would be no data “hidden” with only one failure. Basically, if you can browse the share, you can see everything on it (unless you have shares that are not public and only accessible via certain user accounts). If you do want to replace the dead drive, any drive with a capacity of 2TB or more will do. I’ve tested up to 10TB drives in my Drobo FS. The only caveat is that you must not under any circumstances use an SMR drive (Can I really use any hard drive I want in Drobo?).
I hope that helps!