What happens if you format a drobo as 4TB and fill a disk pack and then take that disk pack out and then have a second drobo that was formatted as 2TB, what happens when you put the first disk pack in the 2nd drobo formatted as 2TB, does the second drobo change to 4TB or does it create 2 partitions of the original disk pack?
its the disk PACKS which are formatted, not the drobo, - they will keep whatever formatting you put on them originally, regardless of which drobo you place them in. If you format a disk pack as 4TB, it will stay as 4TB, if you format a pack as 2TB, it will stay as 2TB even if you put it into a drobo which previously had a 16Tb pack in it.
cheers. That’s put my mind at rest
happy to help 
yeah but what happens if you put both disc packs in a 8-slot Drobo Pro and switch it on?
i would expect… but i havent tested and im not about to…
it will look at the disc in slot 1, load the pack information, it will then load the rest of THAT pack and mount it…
then it will go oooh - more disks - and wipe the next pack and add them into the first pack. (exactly as it would have done if you had let it boot with just noe pack in - and then started adding the next pack disk at a time - if you have 1 mounted pack, and new disks which dont belong to that pack get wiped and added to it. (obvioulsy it doenst actually wipe them - that would take ages , it just ignored what is on them and quickformats them to add to the pack.)
this is justs conjecture.
alternatively:
it MAY look at the pack information on every disk during boot - realise there are two complete packs in there, and come to a screeching halt with an obsecure error (i dont think they would have coded for this possibility though so i cant picture this happen)