Your last image is the explanation.
Despite the 30TB of HDD capacity that you have now loaded in your Drobo, when your Drobo was originally set up it was only provisioned for 16TB maximum volumes. With more recent firmware updates, this has now been increased on the 5D3 to a single 64TB volume. So what you’re seeing is normal, and what happened is you progressively added capacity which exceeded the original 16TB set volume size, so Drobo created another volume for you to use. This is known as ‘thin-provisioning’.
The volume size is set when Drobo was first initialized, and cannot be changed unless you do a complete factory reset, which of course would also erase your data stored on it.
If you want to only have data stored in 1 volume, you would need to:
Copy off your data to external HDDs (14TB+)
Ensure your Drobo has the latest firmware installed
Perform the full factory reset of your Drobo
Confirm on your Dashboard that you have a single volume (equal to your HDD array capacity as loaded)
Reinstall your data.
Alternatively, if you wanted to run 2 volumes, you could format the second volume, but you would be limited to 16TB Capacity (in both) minus data protection - and that would depend on how it magically utilises the variety of HDDs you have currently. If you swap-in larger HDDs later on, again the Drobo would create yet another 16TB volume and on it goes. Each volume would show up on your computer screen as a separate icon (as separate external HDDs) and you could also move data between them.
Good Luck - probably not what you wanted to read, but you will run out of storage capacity on the first volume again shortly and wonder why.