My Drobo had a chunk of free space, and all was going well with it. I looked at my Linux desktop and I'm using about 1 T for my email and photos and intermediate projects. Lot of data there. Be a shame if anything happened to it. I had 2 T free space on the Drobo, and 1 T of desktop data. That's a no-brainer. I set up space on the Drobo and created an rsync script and I backed up my desktop to the Drobo.
First, safety. It's backed up. That's really good.
Second, yellow warning. The Drobo filled up one of the 3 T drives first, turned the indicator yellow and suggested I replace it with a bigger drive. It didn't say anything about the second 3 T drive.
I now have 1 T free space on the Drobo. That's not likely to change for a while. So I'm going to accept the yellow warning for a while, like maybe a year. A lot of my intermediate projects on my desktop will come to completion and be cleaned up and removed. That will reduce the space required.
But I'm all backed up. My data is pretty safe. I'm pretty happy with that.