Hst 4.2 Availabilty percentages and intervals

Hst 4.2 Availabilty percentages and intervals

1. Availability Levels - SLA

   • Uptime in period of time in month/year
     • 99,8%
     • 99,9% (3 nines)
     • 99,99% (4-nines)
     • carrier grade availability = extremely high availability
       • 99,999% (5-nines)

2. MTBF = Meam Time Between Failures

   • average time that passes between failures
   • expressed in hours, how many hours will the component or service work without failure
     • MTBF = (see boek page 55 for example.)

3. MTTR = Mean Time To Repair

   • which is time to take to recover from a failure
     • manual actions
       • components repair
         • notifications of the fault
         • processing alarm
         • find root cause of error
         • looking up repair information
         • spare componenets from storage
         • technician to datacenter for repair
         • restarting and testing the components
       • components replace

4. Availability =

   • • calculation example see boek page 56-57
   • serial availability
     • when a failure of any part in a system cause a failure of the system as a whole
       • system with serial components
       • to increase availability
         • Two systems in parrallel

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