Thanks, everybody, for your info and advice in response to my disk
hanging question.

Ralph Campbell's suggestion sounded plausible, and real easy to try, so
I gave it a try.  Haven't had the problem (nor any other) since (it
might still be too early to tell, tho).

> I have seen this on 4.4 systems. It usually has to do with old disk drives
> (like the RZ23) that can't handle large SCSI transfers. Try
> 	sysctl -w debug.doclusterread=0
> 	sysctl -w debug.doclusterwrite=0
> to disable clustered disk I/O. It could also be a bug in the sii driver
> but without a SCSI logic analyzer, I couldn't find it.

FWIW, the disk drive in question is a Micropolis 1578 (~330 Mbytes)
taken out of a Data General Aviion of c. 1990 vintage.  I suspect it has
some DG-specific microcode because 'DG' appears in its ID string, as
well as 'Micropolis', but it's just like my RZ55 Ultrix disk except for
the labels and the color of the faceplate.

Thanks, again, Ralph and everyone.


-- 
Ted Spradley                tsprad@metronet.com             +1-214-484-5356
Brisco: "...the more I learn the less I know."
Bowler: "At the rate we're learning things we won't know nothing in no time."