99.9% uptime

[Peter J. Holzer]

On 1999-10-15 22:46:22 +1000, Hall, Ken (ECSS) wrote:
> 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.
>
> Quote below:
>
>>  OK, now what does a 99.9% uptime guarantee mean? Well, it means
>> that at bottom, a guarantee that the machine will not be down for
>> more than one one-thousandth of the time. If we assume that we have
>> a stable system, ie., one where the system is not taken down for
>> software upgrades, etc.,

I think this is a big assumption. Apart from the occasional crash in the
evening which wasn't noticed until next morning, all our long downtimes
in the last few years were caused by software or hardware upgrades (and
with the large HP-UX servers, were are generally in the 99.9% range).
Basically, I think a guarantuee of 99.9% uptime is a guarantuee that
you won't have to upgrade/reinstall more than once per year.

You will also have to consider that users generelly aren't interested in
a running OS but in some service. So if I have to shut down samba for
half an hour to enlarge some file system, that's half an hour of down
time as far as my users are concerned. 

	hp

-- 
   _  | Peter J. Holzer             | Nobody should ever have to be
|_|_) | Sysadmin WSR / Obmann LUGA  | ashamed if they have a secret love
| |   | hjp at wsr.ac.at               | for writing computer programs that
__/   | http://wsrx.wsr.ac.at/~hjp/ | actually work.  -- Donald E. Knuth
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