Drobo 5N running low

Hello All.
I hope someone can help me with this issue. I have been using a mac mini for the past few years to use as a media player using plex. It is directly connected to my Drobo 5N. The Drobo did have 12TB x5 installed with 128GB mSATA. The Drobo dashboard is 3.5.2. In August this year, the Drobo stated that the drive in bay 0 is running very low on usable space although the health is good. Before this issue, the bays were all green and I had 3 blue lights across the bottom. Now it shows that the drive in bay 0 RED. I have recently replaced the drive with a new 16TB drive. It now shows that bay 0 with the replacement 16TB drive is green but now bay 1 with the issue. I can’t afford another drive as it’s taken me this long to get the money for the 16TB. Help with resolving this issue would greatly be appreciated. Thank you in advance. Screenshots of what see.

Screen Shot 3

Adding a single 16TB drive does nothing to increase usable storage capacity. It only adds “protection” space. You need to add at least two drives to see any useful gains.

Thanks for your input. So, can you tell me how I had three blue lights at the bottom for the past few years which I believe represent the space used, then come August it’s now full? I have dual redundancy which I know reduces the capacity but you can’t have three lights then all of a sudden it’s full. I just don’t understand. All data on the Drobo came from a couple of Thunderbolt drives that didn’t have dual redundancy which is why the transfer to Drobo. Once the transfers were completed the Drobo indicated that only 30% of space was used. Where has the 70% gone? Everything was just fine until August.

I can’t answer as to what happened to increase your storage usage, but I can confirm what @AzDragonLord said about adding drives. When you have low overall space on your Drobo, you generally need to add 2 new, higher capacity drives (unless you have “expansion” space on other drives). When you are running in dual disk redundancy mode, you actually need to replace 3 drives in order to increase usable space.
Prior to replacing the drive in bay 0, you probably had about 32.6TB of usable space. After replacing the 12TB drive in bay 0 with a 16TB drive, you will see that this number has not changed. This is normal and expected. When you replace the drive in bay 1 with a 16TB disk, you will still have about 32.6TB of usable space. Again, normal and expected. When you replace the drive in bay 2 with yet another 16TB drive, you will then increase your usable space, probably by just under 4TB.

Use the Drobo Capacity Calculator to estimate how Drobo will use your drives:

Unfortunately, they haven’t yet updated the calculator to include 16TB+ drives. But it will give you an idea as to how it works.

Good luck!



Hi Dom.
Thanks for your reply. I shall dump the data back and start again. I think I only have 30 to 40TB of data anyway, probably a little more. I’m only trying to get rid of all the drives I have. I shall keep you apprised.

1 Like

Hi, Guy’s.
Here I have an update on what’s happening. Here is another screenshot. It shows what is currently on my Drobo. Work commitments are making it difficult to remedy my issue, so this is going to take a lot of time. Stupid Question? If I have 68TB (61TB actual) on my Drobo, how can I have 82TB available as seen at the bottom of the screenshot? My mathematics is a bit below par so, can someone tell me how much do all my folders that you see in the screenshot come to given the total capacity of the drives that I have installed in the Drobo. I’m planning to migrate the folders back to the external hard drives that I had before and reset the Drobo. I shall then migrate the folders one by one back as I also did before the issue occurred. I now have 16TB drives x2 & 12TB drives x3 installed. I’m hoping to get another 16TB drive soon as dom1 indicated, possibly for Christmas.

Pay no mind to what Mac OS (or Windows Explorer, for that matter) says is the capacity of the share. It doesn’t know how to interpret how much space is available on the Drobo’s BeyondRAID array. The only capacity measure you can trust is the one that comes from Drobo Dashboard.

Windows says my Drobo has a capacity of 63.9TB, but Drobo Dashboard states that I have 48.9TB. The Drobo capacity status is the correct one.

I hope that helps!


Hello all.
I trust you are all well. Just an update on my issue. It has now been fixed. See screenshots. I transferred all my folders to one of the 12TB drives that showed as critical after I had formatted it. Reset the Drobo, then transferred the folders back. It’s now as it was before the issue with the added two new 16TB drives that I didn’t need in the first place.

I’ve still not found a definitive answer to my issue as to why the Drobo showed the drives as critical when all the data I had stored on it fitted on one drive in a caddy. I shall keep the 12TB with data on it as a backup. Methinks this may happen again. Thank you all for your input and a Merry Christmas.


Glad to see it’s working as expected (for now). You certainly have a lot of free space to work with. Let’s hope the problem doesn’t reproduce itself.

Merry Christmas!


Thank you, Dom. I shall keep you apprised. All the best.