There's a workaround for what you want to do. What you want to do is, I assume, you want to be able to mount "/mnt/" instead of "/mnt/<disc name>". I myself do not know how to do this (setting explicitly that in the FTP setup results in an error), but I accidentally came across a workaround to it. Basically, you need to setup a new User (and a User Group if you want to have this accessible to multiple clients), lets call it User1 (for arguments sake, and to refer to disc 1). In the field for home directories you will put in something equivalent to "/mnt/Disc1", fill out the rest of the information, and press OK. Create a second user called User2, and this time put in the home directories field "/mnt/Disc2". Until FreeNAS allows you to "pool" all the discs (or select discs) into one FTP login, you will probably have to do the above method.