The Server-Side Pad

by Fabien Tiburce, Best practices and personal experiences with enterprise software

Life in the 99th Percentile

leave a comment »

In everyday life, 99% of something is often just as good as the whole thing. 99% of a hot dog will fill you up. Not so in systems. An application with 99% availability means it will be unavailable on average 1% of the time or 87 hours a year. Downtime is typically not evenly distributed. In fact is is more likely to occur when your systems are stressed, during peak time. For this reason, availability is generally stated in degrees of the 99th percentile, typically from 99.99% to 99.999%. A business should consider how many 9’s it needs and how many it can afford. How many 9’s are needed is usually dictated by the cost and the effect of down time on the business. Will down-time cause damage deemed a) catastrophic and irreparable (eg: loss of life for a medical application), significant (eg: loss of income for an e-commerce site) or merely inconvenient (loss of productivity and frustrated customers for a call center)? While no business wants downtime, 99.999% availability is exponentially more expensive than 99.99% availability. Additional uptime requires expensive investments in software, hardware and networking infrastructure, including load balancers and session replicators. Lastly, any site or application that claims 100% uptime should be treated with extreme caution. No system is perfect. No operator or system administrator is perfect. Even with hot deployments enabled, you sometimes need software updates and planned maintenance windows. A business is often better off expecting “only” 99.999% availability and having contingency measures in place than expecting, paying for and never getting to the ellusive 100% mark.

Advertisements

Written by Compliantia

October 26, 2006 at 10:44 pm

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: