Disk Usage (Capacity) Graphs
Disk usage of a partition should not exceed 85% of full capacity. An abnormally high usage can
lead to fragmented disks. Data is placed on the disks in smaller segments as disk fragmentation
increases.
The consequence of a highly fragmented disk is the need to retrieve the data from several places
when a block of records is requested. This takes both time and additional disk and processor
cycles and increases the load on the disk subsystems, which results in higher utilization and
overall lower throughput. The request for data can usually be satisfied by only one read from disk
on an unfragmented system.
Furthermore, the partition can cease to function until relief is provided as the amount of disk used
exceeds 95% and approaches full capacity. The remedy entails either increasing the total disk
capacity on the partition or minimizing the unnecessary data.
A sudden increase in data usage shows clearly on disk usage graphs. It might not be highlighted
on either the Management Summary Graph or the months to guideline calculations because of
the averaging effect of the regression calculations. This can tend to mask sudden changes away
from the trend in a rapidly changing environment.
PM for Power Systems for IBM i includes trend lines for disk utilization based on the previous
three and six months of historical data, in addition to thirteen months. This allows you to more
easily see rapid changes in usage over a short period of time. This also helps you to evaluate
your growth and business needs based on the most recent information.
What to Look For in Disk Space Usage Graphs
Consider the following when reviewing disk space usage graphs:
Is the utilization close to the guidelines?
Is the trend a rising one?
Two graphs are available to understand the usage of disk space on your system or partition:
Disk Space Usage in % per Day
Disk Space Usage in %, 3 Month Trend
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PM for Power Systems Graph Reference Document