xfsdump and xfsrestore to the rescue! I tried xfs_copy just before I left last night, but when I got back today and tried to mount it, the mount failed. So, I dug around some and found a couple of programs called xfsdump and xfsrestore. One apt-get command later, I had them both, as I didn’t have them before. I used xfsdump -J - / | xfsrestore -J - /new, as found on the xfsdump man page… 51 minutes later I have the data copied. Yay! And it mounts properly! And the best part is shown below:

[tlg1466@argento tlg1466]$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda2             19998656   4253776  15744880  22% /
tmpfs                   257364         0    257364   0% /dev/shm
/dev/sda3            223074000  80541848 142532152  37% /home
/dev/sdb4            108998244  80562312  28435932  74% /mnt/sdb
[tlg1466@argento tlg1466]$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              20G  4.1G   16G  22% /
tmpfs                 252M     0  252M   0% /dev/shm
/dev/sda3             213G   77G  136G  37% /home
/dev/sdb4             104G   77G   28G  74% /mnt/sdb4

I got my 12GB back! I’m so happy.