Using a Drobo for Time Machine Backups

Discussion in 'Mac Accessories' started by m021478, Sep 30, 2009.

  1. m021478 macrumors 6502

    Nov 23, 2007
    Does anyone know if partitioning a Drobo is "necessary" if you're planning on using your Drobo as your Time Machine Volume. I called Data Robotics about this and they weren't even able to give me a straight answer. They did tell me that Apple recommends partitioning the Drobo if you're planning on using it as your Time Machine volume, but they weren't sure why this was recommended (strange that they wouldn't know, if you ask me).

    Here is my current situation:

    I recently purchased a Drobo (4-Bay; Firewire 800) and I plan on filling the Drobo with 4 1TB drives and using it exclusively for Time Machine backups. I have no need whatsoever for storing any additional data on my Drobo other than the data backed up by Time Machine (which would be one reason why someone might want to partition the Drobo... but this is not the case for me).

    Here's the thing that makes me believe that it might be "necessary" to partition the Drobo. When I initially formatted the drives and setup my 4x 1TB drives as a single mounted volume (2.7TB of usable storage space), the Drobo Dashboard utility requires that you choose a specify a volume size by picking a size between 1-16TB, and they recommend choosing a volume size that will be large enough to store all of your files for the foreseeable future. See the image below (photo below was taken with my iPhone and uploaded to the web via the cool new DropBox app):


    Seeing as how it's a 4-Bay Drive and thought I currently have 4 1TB drives in it, I can't imaging ever putting more than 4 2TB drives in it, and so I've specified a volume size of 8TB for my Drobo. Anyone who has ever used a Drobo knows that in the Finder, this volume is listed as having 8TB of usable storage space available, though in reality you actually have less than that (in my case as I stated earlier, my 4x 1TB drives provide for 2.7TB of usable storage space).

    Perhaps the Drobo might need to be formatted so that once the Time Machine backups fill up the 2.7TB of space, that it doesn't inadvertently think that there are 8TB of space available and then it erroneously continues backing up (which would theoretically result in problems). This is just a theory as to why partitioning might be "necessary".

    Can anyone confirm or deny whether or not partitioning the Drobo volume is "required" if I plan on using the Drobo as my dedicated Time Machine volume?

  2. akm3 macrumors 68020

    Nov 15, 2007
    It is wise to partition so that your Time Machine can only take a maximum space. If you don't, Drobo will report to the OS that it has a full 16tb or whatever, and Time Machine will relentlessly fill that space, even though you don't physically have all that space. Your Time Machine will just grow and grow and grow and grow. If you partition it, you limit it to a maximum size, then you don't have to worry about it.

    That is my understanding.
  3. m021478 thread starter macrumors 6502

    Nov 23, 2007
    Is this supposed to happen though... meaning, aren't Time Machine backups supposed to grow and grow and grow until there is physically no way it can grow any larger, at which point it would then start deleting the oldest backups?

    Are you saying that once it gets to this point, it wouldn't start deleting the oldest backups, rather that it would inherently start crashing or erroring, or acting all sorts of funky because it doesn't know it's out of room and doesn't try deleting the oldest backups.. instead it just tried to continue creating new ones?
  4. akm3 macrumors 68020

    Nov 15, 2007
    No, I'm sorry I miscommunicated my point.

    My point is that yes, Time Machine is supposed to grow and grow until it runs out of space. The problem is Drobo is telling Time Machine it has MUCH more space (16 terabytes) then it actually has. Drobo lies to the OS so all the OS sees is one enormous space. Then, if it gets close to filling up it's actual space, it tells you to add more hard drives. So, with Time Machine on a Drobo, Time Machine would never stop adding and adding and adding and Drobo would just keep telling you to put in bigger and bigger drives, while still telling the OS 'All clear! You aren't even CLOSE to 16tb's yet! Keep it coming!'

  5. m021478 thread starter macrumors 6502

    Nov 23, 2007
    So here's an idea...

    If I were to fill my four-bay Drobo with 4 x 1.5TB drives, according to the Drobo Calculator on their site, this would give me 4.1TB of usable storage space.

    Then when formatting these drives I moved the slider to the 4TB position, wouldn't this work out for me more or less perfectly (with the exception being that I would in fact have approximately .1TB (100GB) of extra space available on the Drobo that the Finder doesn't see and therefore doesn't use)?

    Wouldn't following the steps above basically give me a 4TB Time Machine volume with 'Drobo-caliber' RAID protection?
  6. pastrychef macrumors 601


    Sep 15, 2006
    New York City, NY
    The only problem you will have by doing it this way is that you will not be able to enlarge your partition if/when you replace the 1.5TB drives with larger ones. Otherwise, it will work as you described for Time Machine.
  7. akm3 macrumors 68020

    Nov 15, 2007
    Exactly. Doing what you suggest will make the Drobo work great with Time Machine, but take away one of the great advantages of the Drobo of merely popping in more/larger drives when you need more space.

    When you want to pop in 4x3tb drives, you will have to format everything and start over.

    I believe it is easier to let Drobo manage it's space and report whatever it wants, and limit time machine by creating a time machine specific partition or using one of the utilities or hacks that forces Time Machine to use only a certain amount of space. I think there is even a Droboapp for that.
  8. m0no macrumors regular

    Jan 8, 2009
    You don't need to create any partitions with the drobo for your Time Machine backup. You can limit the size of the sparsebundle used by Time Machine and resize it as you need without having to format/repartition.

    "to increase the sparse image size , “disconnect all users” in the airport utility and plug your drobo directly back into a tower or laptop. in the command line:
    $ hdiutil resize -size 1500g nameofsparseimage"

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