Simple Sizing Exercise

The following are a few rough formulas based on a medium usage profile for figuring how many back-end and front-end servers you need, and how much storage:

• Definition of Medium Usage Profile

• Number of Front-End CPU's

• Number of Back-End CPU's

• Amount of Storage Needed

Definition of Medium Usage Profile

For our rough estimates, we are assuming the following:

• All clients are Web clients.

  Therefore, the only inputs to be used are: total number of users, and percent concurrency.

• The average size calendar event size is 2K.

• Each person creates five events or todos per week.

• 80% CPU utilization.

• 900 MHz CPU's

• 1 GB RAM per CPU

• Two years' worth of calendar data stored on system.

Number of Front-End CPU's

The formula is:

Number of CPU's = Number of Concurrent Users divided by 4800

Number of Back-End CPU's

The formula is:

Number of CPU's = 4 CPU's per 500,000 configured users

Amount of Storage Needed

The formula is:

Amount of Storage = 5 emails per week times 52 weeks a year times 2K per email (5*52*2K)

= 520KB per user per year

For the assumed two years of calendar data, 1 MB per user.