DroboPro FS and 6TB Drives

I helped a customer recently that was using a DroboPro FS, a small business NAS (Network Attached Storage) device, that let’s you easily add and swap in drives as your storage needs grow. Three bays had 4TB drives, and five bays had 3TB drives. We needed to swap a 3TB for the largest drive we can, which is 6TB currently. However there was no conclusive documentation on how large of a drive the DroboPro FS will take. Drobo did have an old (also the latest) firmware update that allowed for 2TB and higher, but this isn’t exactly very confidence building when you’re trying the bleeding edge of hdd storage capacity. Furthermore, the Drobo was originally fitted with four 3GB drives, then, the largest drives available. They added single drives as needed, of the highest available over the years. The manufacturer “end-of-lifed” this Drobo despite only being a few years old. Google searches resulted in many of the same questions in forums at the manufacturer’s website and elsewhere: what’s the largest drive this will take? Well, the best course of action was to buy local and try a 6TB drive. If it didn’t work, I could return the drive and try a 5TB.  And if that didn’t work, well, we know 4TB works as it already has three installed now.  For the benefit of anyone searching for a similar answer, yes, the DroboPro FS handles 6TB drives fine! At least a HGST Deskstar NAS that I used does. So I swapped a 3TB for the 6TB. My immediate storage needs were met with the addition, but soon after the Drobo made the 6TB drive usable, and after I copied the data over (the point of all this), I received a warning to upgrade the next 3TB drive (pictured in yellow) as disk space was low again.

droboThis was to be expected though. One can use Drobo’s space calculator to see what drive configuration yield what kind of capacity. Before buying the 6TB drive, I used Drobo’s Capacity Calculator. By doing several if-then scenarios, you can understand how Drobo maximizes your different configurations. It does seem one should have even numbers of the same drive capacity, but the BeyondRAID they use is their own black box magic and is hard to say. The 6TB I just added will not be fully utilized until I add another 6TB drive. I then won’t need to replace any more drives for a while. The 6TB are expensive, but a better deal to buy 2 drives, versus four 5TB, for future expansion. The next 6TB we add will be cheaper in a month and will maximize the 6TB drive just added, but using all its reserved capacity.

drobo 1

Original customer configuration


After replacing one 3TB drive with a 6TB.


Next step is to add a second 6TB. Notice no more purple in the Capacity chart. The first 6TB drive’s reserve will be maximized.

What other drive models have you found to be compatible in the DroboPro FS?  Please post your comments below. 8TB are just now starting to come out, but are at an extreme cost premium.


4 Responses to DroboPro FS and 6TB Drives

  • Martin J. Stadler, B.Sc.Eng. (TE) says:

    I think the eight bay Drobo Pro FS can handle drives > 4TB,
    and some of Drobo staff members WILL confirm this when pressed,
    others will deny it, ….. BUT

    there is a major problem with the old Linux file system which
    CANNOT handle volumes over 16 TB !

    Since the DROBO-FS-Pro only allows the creation of 2 volumes, this limits the theoretical max to 32 TB,
    and what’s much worse, the only way to balance the data load across the volume boundaries is to manually
    and physically COPY/MOVE the damned files from volume 1 to volume 2 via the network and computer.

    There is no way I know of to move the files between volumes internally.
    The physical move can take several WEEKS !!! and place a tremendous load, wear and tare on the drives
    Better have dual drive redundancy before trying it.

    Better yet, get a Synology box.

  • Mr T says:

    Thanks for info about 6GB drives

  • AnonAnon says:

    Not so fast, it’s a little more complicated:
    1) The DroboPro FS is logically divided into TWO volumes.
    2) Maximum single volume size = 16 TB, due to the particular Linux partition type size limits.
    3) Therefore maximum total size = 2x 16 TB = 32 TB.
    4) I have previously hit this 16 TB volume limit, which generated warning messages, and I had to migrate data from volume 1 to volume 2,
    via the network attached computer, in order to re-balance the load. (a royal pain, taking several days, also an increased risk of data loss
    or corruption while the data was in transit, due to “bit rot”, undetected network errors, RAM errors, CPU errors, alpha particles etc.)

    5) Note, that any data transfer errors generated outside of the Drobo during the volume re-balancing may have slipped by undetected.

    6) Of much greater concern is a poorly documented BUG in the original design, which was apparently only partially addressed in the
    (second to last) BIOS upgrade: Silent data corruption when the TOTAL number of drives exceeds 32 TB. The documentation does
    not say whether the 32TB limit applies to available user space or total disk space (!!!)

    I speculate this may be the result of some sort of “catastrophic” internal address “wrap around”, but the nice people at DROBO
    are unable or unwilling to provided technical details as to what actually causes it. Some tech support persons insist the model does
    not support drives over 4TB. Other say it does “but no guarantees”.

    7) The related BIOS upgrade documentation is beyond inadequate, the tech support staff give contradicting information, if any.

    8) It is unclear what happens, what causes the error, what internal limit is the problem, and what is actually fixed by the BIOS update:
    a) Exceeded 16TB volume address ? (logical)
    b) Exceeded 32 TB total address ? (physical)
    c) Exceeded AVAILABLE space limit >32 TB, not including space used for data protection and/or reserved space for future expansion.
    d) Exceeded TOTAL drive space >32 TB, including all of the above, i.e. AVAILABLE+RESERVED+PROTECTION+OVERHEAD > 32 TB ???

    e.g. what happens when you insert 8x 6TB = 48 TB drives in the machine with dual redundancy?

    a) Does the system always fail because total number of drives > 32 TB ??
    b) Does the system fail when the amount of DATA actually stored > 36 TB (6 drives used for data, 2 for redundancy) ??
    c) Does the system fail when the amount of DATA actually stored > 24 TB (maximum expected space with 8x 4TB drives) ??
    d) Does the system fail when the amount of DATA actually stored > 20TB (32 TB design max – two drives) ??

    Does the system randomly fail due to address wrap around long before any of the limits are reached??
    No one, I mean no one at Drobo has a consistent answer to this.

    I once had a similar issue when I put a 128GB u-SD card with adapters into my Canon camera designed for a max of 64 GB CF card.
    Lost/corrupted half of my pictures. You don’t want that to happen to a DROBO !!!

    The volume and storage limits are determined by the original formatting of the disk pack.
    Transferring an existing disk pack from an older Drobo to a newer one WILL transfer the same volume limits,
    such that the new DROBO will not be expandable to reach its design potential.

    Old disk pack —–> newer DROBO = same old limits, no gain in storage, unable to replace drives with bigger ones, unable to add bigger drives.
    Old disk pack —–> newest DROBO = not compatible, loose all data.
    newest DROBO + brand new drives = more storage, but must transfer all data via network (takes several weeks of DISK thrashing)

    Thinking about SYNOLOGY !!!

  • MB says:

    Thanks for this info. My Drobo-FS still runs fine and was wondering if 6 TB would work in then. Glad to know it will !

Leave a Reply

Your email address will not be published. Required fields are marked *