Hardware compression w/ Ecrix tape drives?

[Hal Pomeranz <hal@deer-run.com>]

OK, I'm probably missing something obvious here...

I've got an Ecrix VXA tape drive connected to my OpenBSD 2.8 server
and I want to write tapes using the "compressed" mode on the Ecrix
drive (max 66GB/tape instead of 33GB/tape for "standard" mode).
How do I select compression for the drive in software?  I want to be
able to switch back and forth at will, rather than re-jumpering the
drive to change modes.

I'm not finding anything in the st(4) or mt(1) man pages or in
the mailing list archives (the Ecrix support pages barely even
hint about BSD OSes).  Help!

--Hal