IT Infrastructure IT4089 PDF

IT Infrastructure IT4089 JAVERIA NAVEED Availability Concepts – Introduction Availability measures how consistently a system is operational and accessible. “The ability of a system to perform its required functions at a given moment or over a defined period."  High...

IT Infrastructure IT4089 JAVERIA NAVEED Availability Concepts – Introduction Availability measures how consistently a system is operational and accessible. “The ability of a system to perform its required functions at a given moment or over a defined period."  High availability (HA) is essential to avoid disruptions, financial losses, and customer dissatisfaction. Key goal in IT infrastructure: ensure continuous access to resources and services.  Everyone expects their infrastructure to be available all the time  A 100% guaranteed availability of an infrastructure is impossible  Calculating availability  Availability can neither be calculated, nor guaranteed upfront  It can only be reported on afterwards, when a system has run for some years  Over the years, much knowledge and experience is gained on how to design high available systems  Calculating availability  The availability of a system is usually expressed as a percentage of uptime in a given time period  Usually one year or one month  Example for downtime expressed as a percentage per year: Downtime Downtime Downtime Availability % per year per month per week 99.8% 17.5 hours 86.2 minutes 20.2 minutes 99.9% ("three nines") 8.8 hours 43.2 minutes 10.1 minutes 99.99% ("four nines") 52.6 minutes 4.3 minutes 1.0 minutes 99.999% ("five nines") 5.3 minutes 25.9 seconds 6.1 seconds  Calculating availability  Typical requirements used in service level agreements today are 99.8% or 99.9% availability per month for a full IT system  The availability of the infrastructure must be much higher  Typically in the range of 99.99% or higher  99.999% uptime is also known as carrier grade availability  For one component  Higher availability levels for a complete system are very uncommon, as they are almost impossible to  Calculating availability  It is good practice to agree on the maximum frequency of unavailability Unavailability Number of events (minutes) (per year) 0– 5