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Re: Debian hotswap and 5 9's

On Tue, Dec 10, 2002 at 10:46:43PM -0800, nate wrote:
> John Griffiths said:
> > having said that anyone who's todding "five 9's" around as a phrase
> > probably wants to do something a bit more demanding.
> either that or they don't know what they are talking about. my
> previous company it seemed everything was "critical", but in reality,
> it didn't matter if there was on the order of say 20-30 hours a year of
> downtime on most servers. I mean, even our most critical servers
> were down for more then 2 weeks while they were moved from washington
> state to new hampshire on a truck. How many centuries to attempt to
> regain 5 9s of uptime after that? :)

I once worked for a company that produced software for telephone systems
where the requirement was six nines uptime, that is at most 30 seconds
downtime a year. Interesting stuff - at that level you get into having
multiple redundant devices constantly sharing all their state which can
hot-failover within a couple of seconds.

On the telephone system the uptime level is a government requirement, at
least in the US. I'm told that Sprint was hauled up before Congress one
year for having 90 seconds downtime rather than 30.

> the places that I have worked at probably aim for 95% uptime to be
> minimum. not sure how many hours or days a year of downtime that
> calculates to ..

About two-and-a-half weeks. You really don't want to be dropping below
that. :)

Colin Watson                                  [cjwatson@flatline.org.uk]

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