As part of planning configuration changes, you can also consider
your service level objectives or quality of service goals.
For example, as shown in Figure 2–5, CPU utilization has
one peak at 8 CPUs, with many lower peaks. If you configure your system
to always meet the demand of this single 8–CPU peak, you require
100% capacity all the time, you must keep 8 CPUs in your configuration,
and you cannot add new processes.
| 1 | Peak value over the examined
time interval. Value for 100% utilization. |
| 2 | Value for 99.9% utilization. |
| 3 | Value for 99% utilization. |
This utilization graph shows three months of data. As there
are 288 data points per day, there are about 26,000 data points in
the quarter shown. The 99.9th percentile, the value for which 99.9%
of the data points are below that value, is the 26th highest reading;
the 99th percentile is the 260th highest reading. Thus, if you set
your requirement at the 99% percentile (260th highest peak), five
CPUs might be sufficient. With Capacity Advisor's visualization and
reporting tools, you can make a considered estimate of server utilization
using different scenarios. Such estimates can help you minimize overspending
for capacity you use rarely, and maximize utilization of your systems
to ensure that your systems have the capacity needed at the level
you require.
Additionally, with utilization graphs and associated reports,
you can identify how to optimize use of your servers by examining
your quality of service requirements. Capacity Advisor reports provide
additional detail to connect utilization graphs with specific quality
of service metrics. For additional information, see the report examples
in “Producing Graphs and Reports” later in this document.
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