Many apologies -- there seems to be some kind of bizarre physical problem
with the drive I was testing.  It is now performing similarly under NetBSD and
SunOS.

For the curious of mind (and intrepid of heart) I'll note that I've seen some
weird disk problems, but never before a drive that runs five times as fast
when mounted vertically as when mounted horizontally.  I think this one's
going back to the factory...

Thor