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.

1 Answer 1


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.

  • It's a Time Machine volume. When I originally created it, I purposely made it smaller than the largest possible capacity, so that TM wouldn't try to use more storage than I physically had. So now I added bigger drives, and the article is telling me that I can't make that partition bigger without copying my data to another drive, reformatting with the dashboard, and then copying it back. Even if I had a spare 5.4 TB "drive" lying around somewhere to copy the data to, it would take a month to copy the data over and then back.
    – Morrie
    May 6, 2017 at 20:16

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