I bought a Mac Mini earlier this year and as most Mac Mini owners, the internal drive is too small. So I added a 1TB SSD to a Acasis case (the mini Mac Pro lookalike-case) and followed all the instructions on how to move the Dropbox folder to the external drive.
Since then it's been a nightmare. My Dropbox account has about 1,5 TB in it so I don't sync everything but my music folder has to be synced since I'm a DJ. So I have maybe 750GB on the 1TB drive.
But after a week Dropbox stopped working and syncing. And the SSD was full. Very weird. Restarts and re-installation of the Dropbox app didn't help. I had to remove files from the drive and then it started indexing, registering and syncing again. But I had to, again, select which folders not to have 'offline'.
It worked for a week or two, then the same problem. Again. Exactly the same. Solved it the same way. Worked for a couple of weeks. It's getting a bit tired.
It looks like the only way to solve this would be to get a bigger SSD, at least 2TB.