Space Available wrong

Today I bought new drives for my 5N, my current were getting pretty old. I went ahead and backed up all my data, reset the Drobo and started fresh. I figured that would be a lot less time than swapping each drive and waiting.

Anyway, My issue is that I put in five 3TB HGST NAS drives, using dual-disk redundancy. I should have 9TB free, but SMB and AFP both show 17.5TB free. Even with no redundancy, I only have 15TB. What’s going on here?

What does dashboard say you have

SMB may be incorrect due to thin provisioning

The dashboard correctly shows 9TB