rsync backup question

["Thomas H. George" <lists@tomgeorge.info>]

I partitioned a 1 TG usbdrive as ext3, mounted it as /usbmem and entered
the command rsync -r / /usbmem.  The tranfer proceeded with many
messages "skipping non-regular file 'foo'".  Eventually the transfer
hung up with some messages "file has vanished 'foo'". I aborted with a
ctl-c.  df -h reported 

Script started on Thu 21 Jul 2011 06:08:03 PM EDT
dragon:~# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sdc1              71G   48G   20G  72% /
tmpfs                 2.0G     0  2.0G   0% /lib/init/rw
udev                  2.0G  276K  2.0G   1% /dev
tmpfs                 2.0G     0  2.0G   0% /dev/shm
/dev/sdb5              44G  181M   42G   1% /i386chroot
/dev/sdb6             276G   76G  186G  30% /data
/dev/sda1             1.7G   35M  1.6G   3% /temp
/dev/sda5              27G  4.9G   21G  20% /storage
/dev/sdd1             917G  101G  770G  12% /usbmem
dragon:~# exit

Script done on Thu 21 Jul 2011 06:08:14 PM EDT

Clearly most of the files have been transfered and I can read them on
/usbmem.

My object had been to backup everything before moving from Squeeze to
Wheezy

Any Suggestions?