Comments on: Is 100% uptime really possible?

By: Xaprb

Xaprb — Tue, 31 Jul 2012 23:43:09 +0000

By the way, some diligent readers of this blog might have noticed several hours of downtime a couple weeks ago while I messed around with DNS. Thank heavens this blog isn’t a critical resource, or I would have learned what I was doing before doing it…

By: Xaprb

Xaprb — Tue, 31 Jul 2012 23:42:07 +0000

mr. stobbe,

Not quite. You mean to say that as time approaches infinity, probability approaches certainty. You are slightly misquoting me: I said that in the time extending from now to infinity, chance becomes certainty. (I should have said it IS certainty, not BECOMES certainty.)

I am treating now-to-infinity as something that exists, not something that unfolds. The time from now to infinity is infinity, not “approaching” infinity. Make sense?

By: mr.stobbe

mr.stobbe — Tue, 31 Jul 2012 22:24:11 +0000

“If there is any chance at all of downtime, then in the time period extending from now to infinity, the chance becomes a certainty.”

Not to be super-nerdy-math-guy here but the probability infinitely approaches certainty, but doesn’t actually reach it. If the probability isn’t 100% to begin with, then it’s impossible to reach 100% regardless of timeline. Mathematically, it is wholly possible to flip a coin an infinite number of times and always come up with heads. Of course, that’s just me being nerdy and your practical point is valid (99.99999…to infinity percent is practically a certainty).

By: Maciej Wiercinski

Maciej Wiercinski — Tue, 17 Jul 2012 22:56:40 +0000

One can safely promise 100% SLA and simply refund for the the time of outage like a lot of companies out there (so yeah, 1% refund for 99% of uptime). Make sure you always read the small print…

By: hartmut

hartmut — Sat, 07 Jul 2012 10:14:13 +0000

The avialability formual was of course supposed to read

Availability = MTBF/(MTBF+MTTR)

and not the other way round.

Thanks to Axel @MPAB for spotting and pointing it out.