diskutil and df show different sizes I had a failure trying to repartition an external drive (a Drobo array) using Disk Utility.  Now Disk Utility says my drive is 8.8 TB, but it has only one partition on it using 5.4 TB using up "all" of the space (according to the pie chart).  I've been trying to increase the size of that partition to 6.4 TB with no luck.

diskutil shows this:

/dev/disk3 (external, physical):
 #:                       TYPE NAME                    SIZE       IDENTIFIER
 0:      GUID_partition_scheme                        *8.8 TB     disk3
 1:                        EFI EFI                     209.7 MB   disk3s1
 2:                  Apple_HFS Drobo Time Machine      8.8 TB     disk3s2


But df shows this:

/dev/disk3s2   4.9Ti  4.9Ti   26Gi   100% 13373254 4281594025    0%   /Volumes/Drobo Time Machine


Why is one showing me 8.8 TB while the other shows 4.9 TB?  How can I increase disk3s2 to use more of the physical drive?  Obviously I don't want to use all 8.8 TB because I don't really have that much physical storage.  But I do have more than 6.4.
You can't format a Drobo with Disk Utility. You need to use the Drobo tools - 
see this tech note

Key part:


  Although some utilities (such as Apple's Disk Utility in OS X 10.5 and
  later) allow you to repartition or dynamically repartition a volume
  without losing data, Drobo device volumes do not support these
  utilities. Drobo storage device volumes should not be repartitioned
  using any application other than Drobo Dashboard. If you repartition a
  Drobo device drive using a third-party utility (including OS
  utilities), you risk losing the data on the drive.