Disk Mirroring (was Re: Altos 5000)

[Brandon S. Allbery KB8JRR/KT]

As quoted from <3895 at altos86.Altos.COM> by dtynan at altos86.Altos.COM (Dermot Tynan):
+---------------
| In article <1990Aug27.183821.13518 at ico.isc.com>, rcd at ico.isc.com (Dick Dunn) writes:
| > I've seen as many motherboard and controller
| > failures as disk failures.  I don't pretend my experience is typical, but
| > suppose that it might be.  The disks are not the only failure points in the
| > system.
| 
| I suggest that you have some serious design flaws here.  See Law (i).
+---------------

ISC doesn't make hardware.  That's the key to this discussion; you're
discussing apples and oranges.  I've seen many a Taiwanese clone motherboard
and disk controller die in my time.  I've also seen some Altos CPU boards and
file processors die --- but only about once a year (over some fifty systems
that I am de-facto system administrator for) and generally on older equipment.
Not that the integrated approach automatically makes such problems rare --- I
saw quite a few hardware failures on the Plexus equipment I used to manage ---
but when done right, the integrated approach minimizes such problems.  Altos
has had its problems, certainly; the best hardware and software won't help
when it's not appropriate for the market, which has been one of the biggest
problems I've seen with Altos, but the 5000 series looks like it can/will
address many of those problems.

This much I will say about Telotech, Inc. and Altos:  we're picky.  In
particular, *I'm* picky; if Altos hardware and software weren't up to snuff,
I'd recommend dropping it, with a pretty good probability that it would be
done.  But I haven't, and we haven't, because it works.  (I'm technical, not
sales; I could care less about hype, all I care about is if it works.)

+---------------
| > In this case, I'm not arguing that
| > mirroring is worthless, but I do argue that it's inordinately expensive
| > and only addresses one small part of the overall reliability problem.  A
| > single system with mirrored disks on one controller has only one element of
| > redundancy.
| 
| A third time:
| 	MTBF(controller) >> MTBF(disks)
| 
| What exactly do you mean when you say "expensive".  Since Altos doesn't charge
| anything for disk mirroring, and for the most part, is developed in conjunction
| with disk striping (which is worth its weight in gold), doesn't require any
| noticeable NRE.  As for its performance expense, this is *only* borne by those
| who enable it (SCO and C2 could learn something here :), therefore, there is
| *no* expense to those people (the majority, probably) who don't use it.  For
| those who do, you've failed to convince me that the performance expense is not
| worth the gain.
+---------------

I've said enough on SCO and C2 security, so I'll let that one pass.

Granted, most people won't care about disk mirroring.  None of Telotech's
customers, with perhaps one exception (and that only in the long term), will
care about it.  But Ti Kan mentioned airline ticket systems and ATM systems.
In the one, disk mirroring prevents major frustration to employees and users
(think about that next time you're waiting for a plane ticket...) and in the
other, I would consider it essential.

And mirroring is truly *optional*:  it costs NOTHING if you don't enable it.
I've been evaluating an AMS-5000 at work; I'm happy with it, modulo the stuff
Altos has no control over (C2...).  If I weren't happy with it, I'd not be
complaining about C2 security --- I'd be installing another computer in its
place.  Again, I care nothing about hype or "brand loyalty", I care about
machines that do what they're designed to do.

++Brandon
-- 
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