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BleaghBleaghPosted Apr 19, 2012 13:49 UTC (Thu) by nye (guest, #51576)In reply to: Bleagh by jd Parent article: PHP: a fractal of bad design (fuzzy notepad)
>Definitions are close to what are usually used:
> "Mission Critical" - seven 9s reliability as being a minimum
I'd say that's pretty far from 'usually used'. Nearly nothing has seven 9s reliability. That's 30 seconds of downtime per decade - even applications which are literally life-or-death don't generally manage that, and the overwhelming majority of people using the phrase 'mission critical' would mean at least two orders of magnitude less reliable.
'Real-time', as you (sort of) say, has too many definitions to be especially meaningful without qualification. I've always been a little confused by 'soft real-time'. It generally seems to mean vaguely 'low-latency'; which is largely orthogonal to real-time. I guess it's really intended to mean 'general purpose' as opposed to 'batch mode'.
Either way it sounded like your earlier post said that a system can't be both 'real-time' and 'mission-critical', but then later you seemed to say that they can, which is confusing.
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Bleagh Posted Apr 19, 2012 20:32 UTC (Thu) by dlang (✭ supporter ✭, #313) [Link]
"Mission Critical" just means that the organization can't function without it, it says nothing about the required uptime.
for many businesses e-mail is mission critical, but if it's up between 9 and 5 it could be down the rest of the day and not matter. And if it is down during the day and business is crippled, it hurts, but the business doesn't go under.
I can't think of very many companies that electrical power wouldn't be considered "Mission Critical", but very few companies (outside of ones focused on Internet accessible servers) have backup generators and UPS systems, and those don't come anywhere close to 7 9's of availability.
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