Drobo 2ND Generation & 6TB My Experience

A couple of day back, I decided to buy 4 x 6TB WD RED and try them on my Drobo 2nd generation unit as I was not getting answers anywhere if they will work or not! Not even from the local distributor!!

Anyway I went a head and bought them, keeping in mind in case it does’t work I can still use them in my Sinology empty box so it was not a bad investment for me as I use a lot of storage for backing up my videos and high res pictures.

I took all the old drive out and inserted all the new ones, after shutting down the Drobo unit, it asked me first that it will format all the drives and then another screen popped asking me to give names for two volumes, I think this is the 16TB maximum limit per volume thing, it created for me two volumes on the desktop with 17.59TB available as per the mac OS X finder window.

From the dashboard:

In the capacity screen it say total capacity is 24TB and actual is 21.83 but on the bar representation it say 16.31TB and 5.48TB is used for protection? It also deal see everything as one volume.

On the status screen screen it list all the HD capacity (6TB) correctly but then assumes I have only 16.31TB.

On the volume screen it shows that I have two volumes with 16TB max capacity?

I have no clue no what is right and what is wrong her!

I’m using Drobo Dashboard 2.6.4


Jasem Ali

Hi Jasemali,

On my Drobo Dashboard, I have always read the “Capacity” as Total Capacity of the Drobo (excluding Volume Setup).

For example my 5D has 4x 3TB Drives and Dual Disk Redundancy On. So it lists 5.39GB as Total Capacity. Switching to the Usage view, it lists 12TB (10.91TB actual) with 5.5TB for protection which all sounds right.

Manually calculating this. 4x 3TB is 12 TB (10.913 TB actual). For dual disk, 50% available for use and 50% for protection so, 5.456TB for each. Pretty close to what is being reported.

Manually calculating for yours, I get 24TB ( 21.827 TB actual ). With Single Disk Redundancy you should then have 75% available and 25% for protection which works out as 16.37TB and 5.456TB for protection.

So it sounds like that is being calculated and represented correctly.

The Volumes screen also sounds right if it’s showing 2 Volumes of 16TB.

The Status Screen also sounds right.

Keep in mind that Drive Manufacturers use 1000 for their base when calculating capacity. Whereas Drobo uses 1024 as it’s base ( OS’s used to use this as well but I believe Mac OS X is now reporting using 1000)

In summary, it sounds like the numbers are ‘right’.



My Gen2 Drobo is maxed at 4x4T drives with Dashboard showing that I have 2T/19% free space.

Without Drobocal supporting 6T drives, I’m guessing that adding one 6T drive (4/4/4/6) will not get me any additional storage but merely “reserve” some space.

To get an increase in actual storage I’ll probably need 2x6T for 4/4/6/6, correct? I’d have to add the 6Ts one at a time, of course.

Hi MacGui,

I’m not going to comment on the use of 6GB drives, until Drobo indicate the compatibility situation, that would be something you do at your own risk (so I’d recommend backing up first).

With 4x 4TB on a Gen 2 (Single Disk Redundancy only) you should have 12TB (11.17 TB actual) for data storage with the remainder used for protection.

If you increase only a single drive, then you will (as you correctly indicated) increase your protection size. (The rule of thumb is to drop the largest drive in the pack and add up the rest.)

Once you add a second drive you should then see 14TB (13.03 TB actual) for data storage.

I estimate your free space of 19% would grow to 23-24%




Thanks for the response and information.

(I’ve subscribed to this and other threads for email notification, and never get even one!)

Thank you, again.