[m021478]

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?

Thanks!

[mduell]

If you're going to keep the capacity of your Drobo above your Time Machine needs, then going with a 16TB partition is fine. If you're going to let Time Machine fill the entire volume and start pruning older backups, then 2TB is probably the best choice.

[m021478]

Originally Posted by mduell 

If you're going to let Time Machine fill the entire volume and start pruning older backups, then 2TB is probably the best choice.

What do you mean by this exactly. Having 4 1TB drives in the Drobo gives me 2.7TB of usable space. If you're suggesting using the Drobo Dashboard software to configure the volume size of my Drobo with 4 1TB drives to only 2TB, then what exactly happens to the other 700GB? Does that wind up as a separate partition? Are two partitions required? Please explain...

[reader50]

I don't own a Drobo, so this is speculation based on previous discussions. For simplicity of the explanation, lets assume you have an 8-bay model, and are using the first 4 bays with the rest free.

A Drobo allows you to add physical drives as you go along. But operating systems can get confused if a different hardware size is reported, so the Drobo claims itself to be a hard drive already at the maximum size. ie - 16 TB. You have to partition this space down to something within the real size - in your case a maximum of 2.7 TB. The other 13.3 TB are left as free space in the partition table -- in fact that space doesn't exist until/unless you add more drives.

This way, you can add another 1 TB drive later on. The Drobo will notice, and you could used a partition editing tool to expand your volume partition up to the now-higher actual limit. The operating system will now think you have a 3.6 TB volume carved out of the virtual Drobo drive, with 12.4 (non-existent) TB left over as free space.

You can keep upgrading until you run out of drive bays. The operating system thinks the whole 16 TB is there all along, and that it is being allowed to use successively more of that space.

[HenryMelton]

I have three Drobos. My experience is that once your pool of available storage (2.7T in the above discussion) exceeds the set volume size, a new unformatted 'drive' appears which you then format with Disk Utility. All free space is in the pool, and the drives use new space up to their logical size as needed. WIth 4 1T drives and a 2T volume size, Finder and Time Machine and other apps see the logical free space rather than the free pool size.

As the pool size shrinks, Drobo warns you and requests larger drives. Also, as the pool size gets close to the limits, performance slows down. To answer the original question, I might use the 2T logical drives and never put enough on the second logical volume to allow the Drobo to drift into the warning zone.

In my own usage, I use larger logical volume sizes and trim older backup sets manually, but that's just me.

Anyone more experienced is free to correct my statements. I'm on the road and just working from memory.

[m021478]

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?

[mduell]

I misunderstood your question above. Go ahead and make the Drobo volume 16TB, just create a partition for Time Machine to use no larger than the space you actually have. The Drobo volume size is just an abstraction because most OSs don't deal well with storage devices changing size dynamically. With a 2.7TB Drobo or 4.1TB Drobo you could create five 8TB volumes and create multiple partitions on each. Just don't put more data on those partitions than you have actual space in your Drobo.

Originally Posted by m021478 

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

It's sad that I can't tell if "'Drobo-caliber' RAID protection" is a compliment or put-down.

[OreoCookie]

As I understand it, Drobo reports to the OS much more space than is actually available. In that way, when you add more space by exchanging one harddrive for a larger one, for instance, you don't have to do anything. I would just go for the default (I guess 16 TB) and be done with it.

[tooki]

Yeah, but then you have to make sure Time Machine doesn't try to use more than actually exists -- and to do that, making a partition that is no larger than the true available space is necessary.