.. boy, i really hate it when this old lame attribute-caching NFS
`loses' recent NFS writes on block-boundaries. Sorry. Anyway:

>Last, somewhere, (if I can find the docs), there's a PROM test command
>tha

... that  should be able to do a destructive read/write test of the
disk.

But it sound awfully like cabling. we have had a handful of cases that
turned out to be due to marginal internal cabling: the Ultrix SCSI
layer is very, very robust and can cope with error conditions that the
NetbSD/pmax drivers don't.  Replacing the internal cabling with new,
in-spec cabling often cures symptoms like these, at least on 53c94s.