Tuesday, October 16, 2018

Availability - Know your Nines

You scored an interview with a fortune 500 company that has been your dream job ever since you were a gleam in the IT world's eye.  In the interview they explain their environment requires 6 nines and they ask you how you feel about working in a 6 nines environment.  You have no idea what six nines means and you really want to nail the interview so you nod your head and say "it would be great!".  You realize immediately that was a huge mistake...  asking a clarifying question would have been the right thing to do, but now you're stuck and you have no idea what you signed up for!

If you know your nines ahead of time the scenario above could be avoided completely and you can interview like a rock star!
High Availability is a hot topic and most IT professionals are familiar with the concept and understand its importance.  Many have also heard of "the nines" and know it relates to availability, however,  not everyone has taken the time to learn what the actual measurement of each set of nines breaks down to. 

So what do 'nines' mean?  If someone says they need 6 nines of availability, that means they need 99.9999% of uptime each year.  See how that percentage contains 6 nines?  OK, so now that you know the number of nines maps to the percentage of uptime, here is a chart that breaks down how much downtime your system is allowed depending on how many nines are required for availability (*based on a 365 day year*): 

# of 9's     Percentage     Allowed Downtime
6                99.9999          31.5 seconds
5                99.999            5 minutes 15 seconds
4                99.99              52 minutes 36 seconds
3                99.9                8 hours 46 minutes
2                99                   3 days 15 hours 40 minutes
1                9                     332 days

Working in an environment that requires 5 or 6 nines of availability can come with a lot of stress.  If you were not prepared to work under extreme pressure then accepting an offer for this position would be a huge mistake and could set your career back a few pegs.  Even professionals who have the appropriate skillset choose to not work in these environments.  They will often pay more, but they may also impact your quality of life and for some people the money isn't worth the stress.

That being said, there are many companies that strive for 6 nines and they have a solid system that hums along without issue.  If you understand your nines you can be prepared to ask the right questions in an interview to assess if the company is currently meeting their goal for 9's.  From there you can determine if it's the opportunity you've been looking for.

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