Re: Reliability and assurances

["Jack Coats at coats.org" <jack@coats.org>]

I am sure that there are formal academic studies of this, but in
general,

Multiply the probabilities of each thing WORKING by each other,
then you get the probability of the overall system reliability.

The way I see it, it just magnifies why to get a .99999
probability
of something working, you cannot get it with ANY component
having that probability of reliability or less.  Each component
must
be of higher reliability (closer to one) than the desired
reliability.

Five Nines is a reliability goal of some vendors hardware.  To
accomplish this you go to multiple redundant processors, power
supplies, software capable of hot failover, hot-swap RAID disks,
and the list goes on and on.

Does that help? ... Jack