I've deleted a bunch of stuff from my G RAID but it still says "0 KB available" and won't let me
add anything. I know there's something to do so it realizes there's free space. . . but what?
Although "under the hood" each drive, whether internal or external, has its own trash folder, they are all controlled via the desktop as a single trash can. So emptying your desktop trash also empties the external drive trash.
It's possible to empty them individually via the terminal, but that's rarely needed in general use.
If you need more storage, look at the Seagra Technology, Inc Fibre Channel RAID Storage STSRFC4-X which has through put 350MB/sec.
10TB Raw $1899.00 8 TB usable. I think this is ridiculous price for External Fibre Channel DAS RAID Storage, which is SAN Ready. 5 Bay with RAID V.