99.999 (Five nines or Five 9s)

In computers, 99.999 (often called "five 9s") refers to a desired percentage of availability of a given computer system. Such a system would probably have what some refer to as high availability. As Evan Marcus, Principal Engineer at Veritas Software, observes, 99.999 availability works out to 5.39 minutes of total downtime - planned or unplanned - in a given year.

Download this free guide

Limited-Time Download: Sizing Your SaaS Deal Correctly

Most customers fail to accurately forecast their licensing demand which leads to over-and under-buying whereby users squander their negotiating leverage or eat up the discount they earned by buying underutilized shelf-ware. Use this resource to learn how to dodge those potential traps and how to apply deal sizing best practices to optimize your IT spend.

Start Download

• Corporate E-mail Address:

  You forgot to provide an Email Address.

  This email address doesn’t appear to be valid.

  This email address is already registered. Please login.

  You have exceeded the maximum character limit.

  Please provide a Corporate E-mail Address.

• • I agree to TechTarget’s Terms of Use, Privacy Policy, and the transfer of my information to the United States for processing to provide me with relevant information as described in our Privacy Policy.

  Please check the box if you want to proceed.

• • I agree to my information being processed by TechTarget and its Partners to contact me via phone, email, or other means regarding information relevant to my professional interests. I may unsubscribe at any time.

  Please check the box if you want to proceed.

By submitting my Email address I confirm that I have read and accepted the Terms of Use and Declaration of Consent.

In one view, there are three approaches to 99.999 (or even 100) percent availability:

• Special systems that are designed for high availability, such as those from Tandem (Compaq) and Stratus, in which components are duplicated so that a backup component is always available. These tend to be expensive, requiring redundancy of components in which the redundant component is seldom used.
• Shared component systems that are built so that one active system can back up another active system if one of them fails.
• Clustering, a variation of the second approach, in which matched components do not necessarily have to be duplicates of each other