What partition size should I choose?

Quick question which I’m hoping someone can help with as I’ve never really got my head round how Drobo works. If I choose an 8TB partition for example, does the Drobo software manage the fact there’s less storage than that actually available as OS X will see it as an 8TB volume?

Anyway, I have a v2 Drobo with 4 * 1.5TB HDDs in it.

For the foreseeable future, I won’t be replacing any HDDs in this unit and I’m looking to use it as a temporary storage location for some large files. When I’m finished with that, I can re-format it, so I’m not concerned about predicting a larger partition size to cope with growth.

So, what sized partition do I choose for optimum performance?



Try this calculator:

4 x 1.5TB in drobo is 4.1 TB of available space for data. If you want one volume, then I’d choose 8TB.

I have 3 x 1TB + 750GB in my drobo and I have formated it as 4TB volume.

Thanks for that link. I’ll go for 8TB and see what happens!

Why not just go for 16TB and then, as physical drives get larger, all you should have to do is swap them out?

The only reason I could think of going for anything less than 16TB is if you wanted multiple partitions in your Drobo for logical reasons / separation of data (like you wanted Time Machine to use a 1TB partition for backup as an example) or you were using Windows with the 2TB limit in which case you have to do it.

The larger the volume size, the longer it takes for the Drobo to boot up.

@Jennifer, this is not true for OS X. Win boot times grow in proportion to disk sizes, not so in OS X.

@Jennifer, are there any plans to allow users to grow their volume sizes under OS X on non-Pro Drobos? Maybe by allowing the creation of a new, bigger volume and then allowing us to move the data from the original volume over? I’m sure I’m not the only one who made a bad volume size choice at the beginning, and am now approaching the time when the next disk upgrade will create a new volume that I don’t really want.

At this time, Drobo does not support re-sizing of volumes/partitions.

On a side note for personal reasons:
Can I ask why it’s so imperative that users only want 1 volume? I personally have several and like it better. Most of my computer friends have several partitions and would hate to have 1. I just don’t understand the “need” for 1. Can someone explain it to me please?

I’t’s not a need, it’s a desire based on convenience. I have one volume for all my media, of all kinds, because it all gets served up through iTunes on one computer. I could have a volume for Movies, a volume for Audio, a volume for TV shows, etc., I just don’t want to, I’d rather have a single volume with a few top-level subdirectories.

If I can create three more 4TB volumes on my existing Drobo right now, I could move the data around and go to a multi-volume setup, and I won’t need to do any resizing. Can I do that today? Or do I only get more volumes when I add more disk?

From pre-launch days through now it is clear that users want a single bucket of protected storage.

Things have changed over time. Drobo has evolved from a fixed 2TB max volume size to letting users pick a size up to 16TB large. Now Drobo Dashboard is “OS aware” and presents the largest volume size supported by the host OS. Unfortunately volume sizing decisions can’t be reversed – you will get multiple disk volumes of Drobo’s original size as more storage is added.

Is there any way for me to get more volumes without adding more storage, so I can reorganize now?

No, drobo only prompts for more volumes when your available storage size has exceeded your current volume size. Then the new volume will be the same size as the original format size.


Shame, if I could just add more volumes now then I could take the hit once. Now I’ll have to move one thing when I get one more volume, then move a second thing later, etc.

As someone else put it: The larger volume is really for convenience.

I used to (back in the old Win95 days) create the separate partitions for OS, applications, user data, and even the swap file. It never really bought me anything and it was a hassle to manage.

It’s far easier to just have a large partition and have a directory structure that you can dump things into. You don’t have to screw with bumping into what you thought was a reasonable size limit but turned out to be too small, or the shuffling of files around when you need to grow (which is one of the benefits of Drobo and one of the primary reasons I bought it).

For the most part, if you keep things organized into a single directory (like My Documents in Windows or your home directory in Mac / Linux or maybe even having a seaparte ‘media’ directory for photos, video, and music) you can backup your user data just by backing up that one directory tree (or two if you split out the media). If you need to reinstall everything wipe it all out, reinstall the OS, apps, and then restore your user data and you’re back in business. You pretty much have to reinstall the apps, anyway, due to (Win) registry settings.

For me, I don’t see the benefit, any longer, of splitting it all up into separate partitions. Maybe if you had ‘work’ and ‘personal’ stuff but even then I’d just create one large volume and two top-level directories.

Oh, now that I think of it I guess I could see creating a FAT32 partition for compatibility so you could more easily share files across a multi-platform network.

I agree with Brad. Back when I first started with Linux, I used to agonize over how big to make /usr, /home, /boot, /var, etc. Now I don’t bother. I have one small /boot partition just because the boot loader liked to be near the start of the drive (I don’t think even that is necessary any more, then one big / partition with everything in it. As Mark says, one big pool is very much the way to go.

I think I have a (painful) way to get around my particular issue though. I chose a 4TB volume size initially, and now have 4x1TB drives in the Drobo, at 2TB used out of 2.7TB available. When it fills, to get more space I will need to add 2x2TB drives (due to the reserved space you lose if your biggest and next to biggest drive are different).

If I:

  • get USB cases for those two new drives
  • hook them both up
  • copy all my stuff off the Drobo onto them (this may take a while…)
  • reformat the Drobo to 16TB
  • copy all the data back to the Drobo (this will take even longer…)
  • swap two of the 1TB drives for the 2TB drives one-by-one allowing a rebuild between swaps (many hours per rebuild)
    then I can get to a 16TB volume size. I will just have to be super-careful for the time when my data only exists on the two 2TB drives in the USB cases, as it is non-redundant at that point.

This probably will leave me for a week without my data being accessible like it is now. This would be so much easier if I could create a second 16TB volume on my Drobo, move all the data into it, then delete the 4TB volume and rename the 16TB one to the old name!

Just be careful not to have any small partitions less than 1Tb on your volumes. If you do, and you connect via a Droboshare, you will not be able to see and mount the partitions. Keep it connected via USB or Firewire and all is ok, introduce Drobshare in to the mix and you’ll have problems


my thinking goes both ways on this

if you only have 1 large volume… then moving files is “instant”, if you were to try and move a 25GB file from one of your drobo volumes to another drobo volume… it takes a long time with a lot of disk thrashing… with a single volume, it happens in the blink of an eye

however another (possibly old fashioned part of me) worries about volume corruption, and if there is an issue and you have several volumes, then you wont loose/damage as much

Think “freespace consolidation”.

I used to partition disks (when available file systems would change their cluster sizes depending on totall aggregate size), but nowdays I just use one big disk.

“Well, I’ve got 200GB free on this disk, and 100GB free on this disk, and 50GB free on this disk, but nowhere do I have the 300GB free that I need.”

Not a problem if it’s all one disk.

Mine is formatted at 16TB because SATA disks just keep getting bigger and bigger.

yes but drobo consolidates free space across your disks anyway, i think jennifer was saying more why do people want 1 big 16tb volume - when for instance she may prefer 3 or 4 big 16tb volumes, which would still all share the same consolidated real free space

Can you have 4 volumes of 16tb on a single drobo though ?