High Availability Theoretical Basics - Schneider Electric

Step 4: Calculation of the entire installation.
High Availability Theoretical Basics
The following screenshot is the spreadsheet corresponding to the entire analysis:
Note: The only difference between this architecture and the previous one relates to
the CPU Rack: this one is a redundant one (Premium Hot Standby), while the former
one was a standalone one.
Looking at the results of this Parallel System (Premium CPU Rack Redundancy), Reliability
over one year would be approximately 99.9%, compared to 97.4% available with a
Standalone Premium CPU Rack (i.e. the probability for a Premium Rack System to
encounter one failure during one year would have been reduced from 2.6% to 0.1%).
System MTBF itself would increas from 335,000 hours (approximately 38 years) to 503,000
hours (approximately 57 years).
For System Availability, a 2-hour Mean Time To Repair we provide approximately a 9-nines
resulting Availability (almost 100%).
Note: Other calculations examples are available in the Calculation Examples chapter.
Note: The previous examples cover the PAC station only. To extend the calculation
to a whole system, the MTBF of the network components and the SCADA systems
(PC, servers) must be taken in account.
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