Drobo 5D3 Partition wrong size in

The drobo 5D3 has 5 6TB drives in it. The partition listing from diskutil lists it having a 70TB Apple_HFS partition where the dashboard lists capacity as 16.14 TB. with 7.79 TB used with good health. The drive never mounts and it doesn’t appear to be doing a fsck. because I ran ps to check. The volume never mounts. Disk warrior reports that as 70 Tb too. Even if we used Raid 0 you wouldn’t even have 70TB part. You would have a max of 30 TB or less. Can you make some recommendation so we can restore the partition / volume to be able to mount the drive or restore the data?

Can you advise on some further information:

Have you previously or recently upgraded both the Firmware and the Dashboard to the latest versions?
Do you already have an external backup of the data?
Can you turn off the Drobo completely (including power), remove all HDDs (mark them in order) and then restart without HDDs - can you Dashboard see the Drobo?

The 16TB volume is due to a previous (very old) setup and the 5D3 can accept volumes up to 64TB, but to enable this, you will need to reformat the array, and this destroys any existing data. So if you unconcerned about the data, then there is another path to take.

Yes the drobo has the latest firmware and latest dash board.

This is my customers drobo and we can get most of the data one way or the other, but the question remains why did this happen, will it happen in the future and the data and partition recoverable.

No I have not removed the drives and attempted what you have said, but I may. I am aware that the array can be reformatted and like I indicated before we want to know why this happened and if it’s going to happen again, otherwise we may have to use the drobo as a backup to a synology NAS or some other storage.

Thanks for responding,


Firstly, Apple (& DW) does not read the volume sizes correctly for Drobos, so the 70TB report is erroneous.

With the 5x6TB setup a Drobo 5D3 can only offer single or dual redundancy options and not RAID 0, so the effective capacity is only 16TB++ or 10TB++ respectively, based on the array described.

Volumes, once set on a Drobo cannot change size without reformatting, however if a preset volume size is reached (eg 16TB) and more data is added due to available HDD capacity the Drobo will automatically create another volume of the same size which will then appear as a separate drive on the Mac. Most users opt for the 64TB volume setting which allows their HDDs to be upsized and hot swapped as capacity is reached, without interfering with the volume size.

I’m still unclear whether you can read the data on the Drobo, but if you can, it would be best to offload it all, reformat the Drobo array selecting a 64TB volume size and repopulate the HDDs with the data. I have not yet come across any reports of any Drobo that can automatically change its set volume size and still provide access to the data.

My last recommendation is to always maintain a current external copy of your important data, regardless of which RAID machine you use.

EDIT: You did not mention which Mac OS you are using. The more recent Mac OS’s require some manual security setting changes to allow the Drobo Dashboard to work correctly - and there are other posts on this board that cover this situation.

No the drive does not mount, and when we run stellar against the drive it gets a little valid data and a lot of junk which might be typical in file carving versus techniques having access to the file system meta data.

My last recommendation is to always maintain a current external copy of your important >data, regardless of which RAID machine you use.

I agree it’s always a good idea to have redundant copies of important data.

When a Drobo disk pack is created, it is formatted with a 64TiB volume. This is reported as 70TB by MacOS. This way as you grow (add larger disks), you don’t have to reformat every time.
As for your storage, it sounds like you have Dual Disk redundancy enabled. This will mean that you are protected against 2 simultaneous drive failures. But, this reduces the amount of actual storage by the size of the 2 largest drives in the unit. Since yours are all the same size, you lose 12TB of storage (2x6). So you have 18TB (Raw) of storage, which will be displayed as (roughly) 16.37 TiB in Dashboard, slightly less due to overhead and formatting. You always follow what Dashboard says in regards to how full the Drobo is, not Windows or MacOS because they show the ~64TiB figure as how much space is there. They report the volume size, not the amount of physical storage.

Why it doesn’t mount is a completely different matter, but has nothing to do with the reported size. Disk Warrior would be the best bet for recovering the partition information so that it will mount.