This article documents how to add a second drive to your FreeBSD system and format it as UFS.  If you have a system that allows hot-plugging (like the Dell line of servers) then this can be done live without shutting down the server.  If not, then you will have to shut down the server only to insert the drive.  In this article I am going to reference SCSI drive devices (da2) if you have SATA devices, then please not that the device ID will be different (ada2).