Umfriend, I think that you have it, except that your point 2, the 2T drive is part of the pool. This is the only way that I can think of that I can expand a full diskpool. I am not sure how I would delete contents from only the 500GB drive? the whole issue is that I don't have 500Gig of free space in the pool to evacuate the drive.
I do have backups and I suppose that I could just take out the 500Gig drive, without evacuation, put in the 2T drive, add it to the pool and then restore the pool from backups. Is that what you are suggesting?
Reinsert old 2TB drive and hope DP recognises it and all will be fine? This is the part that kind of scares me :-)))
Also, without doing an evacuation of the 500Gig drive, are there going to be any lingering effects that I need to worry about? Is it going to keep asking me to reinsert the drive at every bootup, or anything like that?