So I need to upgrade my hard drives because they're full. This is a backup pool so not worried about data loss here.
Anyhow, when you click remove on a full pool it seems that it doesn't like removing drives no matter when options you pick and appears with the not enough space error in the attachment below.
Not a problem as such as I'll remove the disk, tell it that its gone. It'll forget and I'll then add the new disk, it'll balance and all will be well. Just a heads up in case others run into the strange quirk of a full pool.