tar under SCO Xenix

[Chris Lewis]

In article <3195 at wasatch.utah.edu> kessler%cons.utah.edu at wasatch.utah.edu (Robert R. Kessler) writes:

>We are running on a PS/2 Model 80, using SCO Xenix 2.2.x.  We have an
>Arnet Smartport from which we run a half a dozen terminals.  The problem
>is that when someone does a tar (to our Mountain tape drive), all of
>the devices connected to the Arnet board hang up.  So, we have to have
>everyone log out, do the tar, then everyone logs back in.  SCO claims
>that tar uses so much of the system resources that the Arnet board
>gets lost.
>
>Is this true?  Has anyone experienced anything similar.

The question I have in response is how "hung" do they get?  Bursty?
Or totally dead?  Bursty is typical of many systems with tape drives.
Though, on better systems it should be almost imperceptable.  Full
blown hung is another story:

It's not truly tar's fault - 1/4" streamer drivers are extremely difficult 
to write, many of them will have interrupts disabled (eg: no terminal 
I/O) for relatively long periods of time - in order to get the stupid
thing streaming, they heavily hog the CPU to make sure that they don't
miss the inter-command timing windows (typically a couple of milleseconds
before the tape drive decides to stop and backup).

It *shouldn't* be particularly objectionable - especially since Xenix 
2.2.x tar can't talk in buffers bigger than 32K (or is it 64K? doesn't 
matter...), so you should get slices occasionally.

Does your tape drive do a lot of "shoe-shining"?  If not, well, you'd
best live with the situation - it's so damn difficult (and important)
to keep these drives streaming, that it's worth almost anything to get 
them to do it.  If they do "shoe-shine", I suspect that the Mountain
Driver or possibly the Arnet (tho, I doubt it due to the reviews I've
heard) is doing some disgusting things with the interrupt level or
something.  (I assume that the Mountain driver is not the same as
the Wangtek)  Bitch loudly.  There is a remote possibility that you
have the card's interrupt set wrong, but *those* symptoms are *extremely*
slow tape I/O - which you don't seem to be having.

I've been hearing rave reviews on Xenix 2.3.1 Wangtek tape driver 
performance on 20Mhz or so CPU's, so it might be time to upgrade your 
O/S (especially if the Mountain driver is the same as the Wangtek).
-- 
Chris Lewis, R.H. Lathwell & Associates: Elegant Communications Inc.
UUCP: {uunet!mnetor, utcsri!utzoo}!lsuc!eci386!clewis
Phone: (416)-595-5425