5.1.4.4 Amount of Storage Needed

The formula is:

Amount of Storage Per User = 100 emails per week, multiplied by 52 weeks a year, multiplied by 5K per email, multiplied by the number of years worth of data to keep online, multiplied by the number of copies (5 backups + 1 working copy) kept online = 100*52*5K*2*(5+1) = 65 MB storage per user.

That is 2.6 MB per user per year per copy held online.

The final number depends on how many hot backups or archival backups you keep online. For this example, 5 backup copies was the number used.