Mounting and Unmounting FreeBSD Filesystems
Now, we will see how the versatility of UNIX-style filesystems can really shine. Let's say that your system outgrows its single disk (/dev/ad0), and you install another disk as the primary slave so that it appears as /dev/ad1. (A SCSI disk would be available as /dev/da0, and so on.) After you partition and label the disk (a procedure that is described in detail in Chapter 19), you will have one or more new filesystems you can add to your system's directory structure at any point, like grafting a new branch onto the side of a tree.
Suppose, for instance, that you have a system in which you have been adding new users left and right, and they keep uploading large files into their home directories; ...