Need to Backup Using Dump

[Bill Tillman]

I have two FreeBSD 8.2-STABLE servers running NFS. I have tons of files on Server A that I want to backup to a big drive on Sever B. Server B nfs_mounts one of the filesystems on Server A to /mnt. So if I wanted to make a backup of the filesytem on Server A to Server B I tried:

dump -d /home/my_home/backups/20111024 /mnt

but each time I try this it tells me that filesystem /mnt is unknown. /mnt is not in /etc/fstab. I manually mounted this via NFS and that's where all the files I want to backup are accessible to the command line on Server B. What am I missing?