It’s called “unRAID”. It’s purpose is data redundancy without striping or raid, and it’s a very popular NAS solution because it has many benefits over raid setups.
Basically, Syncthing is putting 82TB of temp files onto a single 8TB drive because the temp files don’t seem to use drive space until after synced. Since the mapped drive (and Syncthing) sees the full 147TB, it doesn’t realize that disk1 is out of space.
A normal file transfer makes folders only as files are copied, and doesn’t make temp files, so it correctly spreads the data across the disks based on my unRAID split settings.
I am just going to have to sync these servers using old school file transfers, and then let Syncthing take over for the day to day syncing. After the big transfer is done, and the folder structure is in place, things will go to the correct disk(s).