The Historical Observations and Growth Rate Reports for channel utilization are shown in Figure 5-7. By studying the detail of the historical observations and looking at the growth rates, you can conclude that the I/O load on the system is increasing slightly in the long term. The short- term growth rates show a very high degree of change. The high variability in the short term, where channel 2 shows an increase of 47.08% in a single month, may indicate some instability in the workload. Looking at actual data, you can see that the load on channel 2 generally runs in the high teens, with an occasional jump into the low 20s, until the final observation, which shows a sudden increase to 30.9%. A sudden, unexplained change is cause for concern when you are trying to forecast from this data since many forecasting methodologies place heavy emphasis on the most recent value of the observed data when estimating the forecast. If the additional load on channel 2 is due to a transient condition, the forecast values will be much too high. You should investigate the reason for the change in channel 2 utilization before you undertake a more detailed study. These reports present historical data with the growth rates, allowing you to examine the behavior of the data before proceeding with the more detailed statistical analysis procedures provided in the remaining chapters. This gives you a chance to judge whether the data provides a good basis for further study.
+----------------------------------------------------------------------------------------------------------------------------------+ |SYSID: TSO1| | | | EXTENDED EXAMPLE --- MONTHLY HISTORICAL OBSERVATIONS | |ZONE: 1 | | |-----------+----------------------------------------------------------------------------------------------------------------------| | | CHANNEL 1 | CHANNEL 2 | CHANNEL 3 | CHANNEL 4 | CHANNEL 5 | | | | MONTH | BUSY (%) | BUSY (%) | BUSY (%) | BUSY (%) | BUSY (%) | | | |-----------+----------------+----------------+----------------+----------------+----------------+----------------+----------------+ | SEP 97 | 5.4 | 18.9 | 18.8 | 7.3 | 15.8 | | | | OCT 97 | 5.5 | 19.5 | 19.6 | 7.4 | 14.8 | | | | NOV 97 | 6.4 | 19.8 | 20.2 | 10.0 | 15.9 | | | | DEC 97 | 5.3 | 18.0 | 18.6 | 8.9 | 14.6 | | | | JAN 98 | 6.1 | 19.0 | 19.4 | 9.0 | 15.7 | | | | FEB 98 | 6.3 | 23.1 | 18.8 | 11.1 | 16.2 | | | | MAR 98 | 5.5 | 19.7 | 16.9 | 9.5 | 14.9 | | | | APR 98 | 4.8 | 18.0 | 15.2 | 7.7 | 14.3 | | | | MAY 98 | 4.6 | 17.8 | 15.7 | 8.2 | 14.5 | | | | JUN 98 | 5.0 | 17.6 | 15.8 | 9.3 | 15.1 | | | | JUL 98 | 6.9 | 21.0 | 18.6 | 11.7 | 17.8 | | | | AUG 98 | 8.6 | 30.9 | 15.0 | 10.7 | 15.4 | | | +----------------------------------------------------------------------------------------------------------------------------------+ +----------------------------------------------------------------------------------------------------------------------------------+ |SYSID: TSO1| | | | EXTENDED EXAMPLE --- GROWTH RATE PER MONTH | |ZONE: 1 | | |-----------+----------------------------------------------------------------------------------------------------------------------| | | CHANNEL 1 | CHANNEL 2 | CHANNEL 3 | CHANNEL 4 | CHANNEL 5 | | | | INTERVAL | BUSY (%) | BUSY (%) | BUSY (%) | BUSY (%) | BUSY (%) | | | |-----------+----------------+----------------+----------------+----------------+----------------+----------------+----------------+ | 11 MOS | 4.40 % | 4.57 % | -2.02 % | 3.63 % | -0.24 % | | | | LAST MO | 23.94 % | 47.08 % | -19.22 % | -8.37 % | -13.52 % | | | +----------------------------------------------------------------------------------------------------------------------------------+
Figure 5-7. Extended Example Historical Observations and Growth Rate Reports: Channel Utilizations
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