Hall, Ken (ECSS)
KeHall at exchange.ml.com
Fri Oct 15 12:44:02 GMT 1999
Sorry, forgot to change the subject on my first posting.
I was reading a comment this morning about something Microsoft had published
to the effect that there were vendors guaranteeing 99.9% uptime for NT. The
guy who wrote the reply did the math for what that means, and the results
are very interesting.
OK, now what does a 99.9% uptime guarantee mean? Well, it means that
a guarantee that the machine will not be down for more than one
of the time. If we assume that we have a stable system, ie., one
system is not taken down for software upgrades, etc., then we are
the time from a system crash (strictly, I think, from the time that
is actually noticed) to the time that the system is running again.
So, below is
a little table that shows the best guaranteed up-times for various
the above restart time, rounded up.
Restart time Uptime
10 mins 7 days
30 mins 21 days
120 mins 84 days
The conclusion I draw is that either (a) NT crashes very often and
to restart or (b) NT crashes less often but takes a long time to
Considering I've had Netware servers and UNIX boxes that stayed up for 6
months at a time, maybe we need to re-think what constitutes acceptable
availability. "99.9%" sounds great, but if you look at it this way, it's
really pretty abysmal.
Anyone care to do the math for their mainframe systems for comparison?
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