NonStop S-Series Planning and Configuration Guide (G06.25+)

Planning for System Availability and Support
HP NonStop S-Series Planning and Configuration Guide—523303-015
10-2
How Availability Is Measured
How Availability Is Measured
HP believes that the measurement of availability should be from the end user’s
perspective. Simply recording that a certain hardware or software component is not
operating is not enough; you must also take into consideration the user’s ability to
access the service, the quality of the service provided, and the acceptability of the
response time to the user.
Although major changes—such as installing a new operating system—obviously affect
availability, the effect of other types of changes might be less apparent. For example,
changing the characteristics of a communications line could cause response time to
become unacceptable to an end user who is trying to use that line to access a file on a
remote system while the change is being performed.
While the computer industry has typically measured availability in percentages, HP
recommends measuring availability by outage minutes in 24-hour-a-day, 365-day-a-
year operations.
Outage Minutes/Year
An outage-minutes/year measurement is easy to understand and provides more
meaningful data than percentile numbers such as “95 percent available.”
Minimizing Planned Outage Frequency
By taking the time to anticipate and plan for changes, you can avoid taking your
system down for unnecessary planned outages.
You can take action now to prevent planned outages in the future in these areas:
•
Evaluating System Performance and Growth on page 10-3
•
Providing Adequate Computer-Room Resources on page 10-3
•
Configuring Your System to Accommodate Future Changes on page 10-3
•
Implementing a Formal Change-Control Process to Manage Change on page 10-4
Percent Availability
90% 99% 99.9% 99.99% 99.999% 100%
Outage
Minutes/Year
*
50,000 5,000 500 50 5 0
User Impact
*
35 days 3.5 days 8.3 hours 50 minutes 5 minutes 0 minutes
*These impacts are approximations.