think of it as your volume is your garage…
the disks you put in drobo are your cars.
the actual data you can store is what goes in the trucks of your cars
if you make your garage (volume) huge to begin with - even if you only have a couple of small cars (so you cant put very much in their boots) then in the future when you get more or bigger cars they will still fit in your garage.
since your first volume (garage ) was small… now that you have bought additional drives (cars) you have had to build a second garage (volume) next to the first garage (volume)
you are still limited by what you can put in the trunks of the cars, it is in no way related to your volumes.[hr]
yes, if dashboard has 938GB free - then you can put another 900gb of data onto drobo. you could add that on to EITHER of your volumes tho.
you could have made two 16TB volumes - and if you put your 2tb of disks into drobo then you could have used 1tb on one 16tb volume and 1 tb on the other 16 volume, or you could have put 1.5tb onto one 16tb volume, and 500Gb onto the other 16TB volume.
the way your drobo is setup - as soon as your actual real physical disk space is greater than the capacity of all your volumes, then t will create an additional volume for you so that you can then access this space.
i…e. if you had two x 2 tb volumes - then you could only put 4tb of data on them. if you added enough disks so that you have 5tb of usable space, then drobo would create a third 2tb volume - so that you had 6 (3x2tb) volumes and you could put 5tb (your real disk space) onto those three volumes however you like.
its called thin provisioning - you make a volume that is bigger than the disk - that way when your disk grows (you put in bigger drives) then you dont need to change the volume since it is already larger enough to take advantage of the additional capacity you have just added