IBM 610 workstation computer 3434

when were were doing ha-cmp ... we talked to the 1-800 people. they had five-nines requirement (5 minutes downtime per year) ... and were using a platform that was hardware fault tolerant. however, the platform periodically required system software maint. ... even doing it only once a year ... they still saw outages on the order of 30+ minutes (using several years worth of down-time budget per year).

the ss7 had a pair of T1 links that it used to talk to the 1-800 lookup box ... and if it failed to get an answer from one side ... it would redrive the same request down the other line (in some sense 1-800 are like domain-host names that have to be looked up to get the real network address ... err, phone number)

a pair of ha-cmp boxes ... one attached to each T1 link could provide the same hardware MTBF as the fault tolerant hardware box ... with the redirve from the ss7 masking any failure-fall-over.

then, there was a proposal to use a pair of fail-over fault tolerant hardware boxes ... in order to maks their software downtime; however going to the expense of a pair of fail-over fault tolerant hardware boxes then negated the purpose of having the fault tolerant hardware boxes in the first place. part of this was that the reliability of basic (non-fault-tolerant) hardware had significantly advanced-improved over the years.

misc. past ha-cmp posts

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