I don't know what, but I have an example, which has been puzzling me for
months:

I have a 4GB, 7200RPM Micropolis wide SCSI disk drive.

Its performance, to say the least, has not been stellar.  No matter what the
testing conditions, I can never get more than about 1.2MB/sec on
writes -- to the raw device, and that on 8MB sustained writes -- and
about 5MB/sec on long sustained reads, from the raw device.

Through the filesytem, or to/from the block device, I get about
2MB/sec on long reads, and about 800KB/sec on long writes.

The real-world performance of the disk is not stellar.  It's a news
spool, and it's a *very slow* news spool -- to the point that people
reading news notice long pauses.  The machine does nothing *but* news,
and it's a 75Mhz Triton-chipset Pentium, so...

I've tried three different SCSI controllers, a BT956C, a NCR825, and a
BT946C with a wide->narrow cable.  (it's a wide disk.)  I've tried
different terminators; I've tried completely shielded internal scsi
cables.

Today, I hooked the same drive up to a SPARC 10 running SunOS, with
the same wide->narrow cable, and got 7MB/sec on writes and about the
same on reads, on the raw device.

Through the filesystem, I got about 6MB/sec on long writes, and
5MB/sec on reads.

That's *five times* the performance under NetBSD -- and the SPARC had
its usual user load, while the NetBSD box was totally idle for the
test period.

To make things even more perplexing, an old 1.7GB Micropolis on the same
NetBSD machine, on the same controller, gets about 3.5MB/sec on reads
and writes raw, and about 2.5MB through the filesystem.

The only odd things I can see about the 4GB disk are a rather large
number of defects, 315, and no support for command linking.  It does
support tagged queueing and disconnection.

Can anyone even hazard a guess at what's going on here?  I have a
$1500 disk drive that's giving me the performance under load of an
RA80 -- but it works fine under SunOS.

I don't mean to throw any stones.  I would just love some help
figuring this out.