16Tb is a limit for the volume size
if you have more actual space than this - then drobo will automatically create a second volume to allow you to put additional data on your drobo (NOTE: this isnt quite right - see the final part of my post below - i forgot you had a drobopro - but still read them all in order anyway
with 24TB of space - drobo will create a SECOND 16Tb volume - and then you can put a maximum of 24tb of data spread across both volumes.
this will be fine up until 32tb of space
when you put in bigger disks to get 33tb of space - drobo will create a THIRD 16Tb volume - and even then when you have 3 x 16tb volumes - so ti looks like 48tb - you will still only be able to put 33 tb (your actual space) across all the volumes[hr]
with older operating systems the maximum volume size is 2tb - so people would have 4 x 500gb disks - for 1.5tb of space - and a 2tb volume and be fine
then they would replace those disks (one at a time) with 4 x 1 tb disks - for 3tb of actual space
and be puzzled why drobo had made a second 2tb volume
but it was so that they could use all 3tb of their real space - which you woudlnt do with a single 2tb volume - but you could with a second 2tb volume.
then peopel still get confused because they have 2 x 2tb volume - so it looks like 4tb of space - but they only have 3tb worth of disk space
but you can put your 3 tb onto your 2 x 2tb volumes how ever you like
so you could fill up one volume and have 1 tb on the other volume
or you could put 1.5 tb on each volume
whatever you like
then when they replaced those 4 x 1tb with 4 x1.5tb - they would have 4.5tb of actual disk space - so their 2 x 2tb volumes still werent enough to let them fully use that space - dso drobo would create a third 2 tb volume
i hope that makes sense?[hr]
BUT - since you have a droboPRO (ive just realised) you can control your volume creation (its automatic on smaller drobos and you dont get a choice)
on your drobopro right now - you can create a second 16tb volume if you want - or an 8 tb volume - you can have up to a maximum of 16 x 16tb volumes - and you could create them all right now if you wanted to!
the total data you put on those volumes can still never be more than the actual disk space you have available - but you can create upto 16 volumes - and choose each of their sizes yourself on a drobo pro