Unix/Linux Pre-Install Questions to Ask and Answer

Capacity planning:

Some vendors will tell you to buy a large number of servers, run the system awhile to see how it performs, and return the unneeded servers for some sort of refund.  But there are other ways to estimate accurately the number of servers required for some service(s) to run and provide a required average response time (sometimes other performance requirements too).  These include:

Without experience, the required mathematical skills, or a huge budget to blow on consultants or needless equipment, you can use queuing theory to accurately estimate the number of servers required to provide some specific response time, by plugging in a few values into a fomula and graphing the result.  There is a formula from Dick Brodine of National Computing Group (DickBrodine@juno.com), reported in the July 2006 IEEE Computer (“Mathematical Server Sizing”, pp. 91–93).  This formula is based on one by Kishor S. Trivedi in his book Probability and Statistics with Reliability, Queuing, and Computer Science Applications, ©1982 Prentice-Hall.  Trivedi's model was designed to estimate response time from a number of factors, assuming a single server.