Ecrix Tape Drive on OpenBSD?

[Mike Darweesh <jaromir_(_at_)_Radix_(_dot_)_Net>]

Hi,

I just hooked-up my Ecrix Tape Drive
(http://www.ecrix.com/products/VXA-1-desc.cfm)
to my OpenBSD 2.7 i386 machine. Unfortunately, I don't seem to be able to
fit my 26GB of data onto the (33GB raw) tape:
# df -k
Filesystem  1K-blocks     Used    Avail Capacity  Mounted on
/dev/wd0a    28808422 25449768  1918233    93%    /

# dump -0 -a /
  DUMP: 76.11% done, finished in 1:04
  DUMP: End of tape detected
  DUMP: Closing /dev/rst0
  DUMP: Volume 1 completed at: Thu Dec 28 15:52:11 2000
(etc...)

Should I start fiddling with dump command line options?
Or are there more things I should be looking at?
I'm new to tape backups.

Thanks,
Mike