Five 9s uptime – how much each 9 matters

Technology Futurist:

“Since I saw Larry Borsato mention some figures in the 99.999% availability requirement-for-VoIP-networks debate, I decided it was time for me to dust off my networking theory book and implement Erlang’s formula on an Excel spreadsheet using VBA, to get a better feel for how much each “9” matters.

Here are the results that I got:”

Availability Associated Downtime per Year
99% 87 hours and 36 minutes
99.5% 43 hours and 48 minutes
99.95% 4 hours and 23 minutes
99.99% 53 minutes
99.999% 5 minutes
Comments (5)

  1. Mark-Allen says:

    Good numbers. I’ve used the same figures during my high-availability and fault-tolerant presentations to show what each increase in percent could cost the company in real money.

    It should be noted that when people talk about these numbers they often put it in the context of "UN-scheduled downtime".

    With technology today, from my point of view, it should be reasonable to ask for 5 nines.


  2. ALEXI says:

    I just found this page in a google search, I’m looking for the erlang formula writen in VBA, if you can help me please I’d really appreciate it.