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Chapter 7. Designing Monitoring and Main... > Monitoring Exchange Server Availabil...

7.9. Monitoring Exchange Server Availability

Nearly all Service Level Agreements (SLAs) have one common component – a measurement of system availability. In very high-availability environments, this is often expressed as "four nines" (99.99%, or less than a couple of hours per year) or "five nines" (99.999%, or only minutes of downtime per year). However, only the exceptionally optimistic or innately foolish would suggest trying for "six nines" (30 seconds of downtime each year, or a reboot every other year, as long as it’s a really quick one).

There are several types of availability (or non-availability), including planned availability and total availability. Total availability is defined as the percentage of uptime over total run time, and can be computed easily by using the information in the System Event Log.


  

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