I've been using Seagate travan drives for a long while under NetBSD, but
only since 1.6 have I attempted to use the ATAPI version as opposed to
SCSI.

The 10/20 drives work OK (STT20000), though setting hardware compression
seems to fail (mt compress 1 gives Operation not supported by device).
However, the 20/40GB drives (STT3401A) don't work under NetBSD 1.6.1 or
-current. They work fine under Windows 2000 using the Seagate diagnostics.

Trying to write a tar file (cd /; tar -cpl .) gives the following
immediately and the tar exits with status 3:
tar: only wrote 5120 of 10240 bytes to /dev/rst0

This is followed by a kernel message:
st0: WARNING: cannot revert to default density

Relevant fragment of the dmesg:

atapibus0 at pciide0 channel 1: 2 targets
st0 at atapibus0 drive 0: <Seagate STT3401A, HP013G4, 310A> tape removable
st0: density code 0, 1024-byte blocks, write-enabled
st0: 32-bit data port
st0: drive supports PIO mode 3
st0(pciide0:1:0): using PIO mode 3

-- 
Stephen