Specifying A Time Base - HP StorageWorks 2/64 - Core Switch Administrator's Manual

Specifying a time base

If you specify a time base value other than
the current data value. Instead, it calculates the difference between the current data value and the data
value as it existed one time base ago. It compares this difference to the threshold boundary limit.
For example, if you specify the time base
between two samples a minute apart. It then compares the difference (current data value – data value one
minute ago) against the preset threshold boundary.
When you set a time base to a value other than
configuring events:
• Fabric Watch triggers an event only if the difference in the data value exceeds the preset threshold
boundary limit.
• Even if the current data value exceeds the threshold, Fabric Watch does not trigger an event if the
rate of change is below the threshold limit.
The following examples illustrate each point.
Example1: Triggering an Event
Figure shows a sample graph of data obtained by Fabric Watch (the type of data is irrelevant to the
example). A high threshold of 2 is specified to trigger an event. A time base of
occurs only if the rate of change in the specific interval (one minute in this example) is across the threshold
boundary. It should be either higher than the high threshold limit or lower than the low threshold limit. As
illustrated on the tenth sample, the counter value changes from 0 to 1; hence calculated rate of change is
1 per minute. At the thirteenth sample, the rate of change is 2 per minute. The rate of change must be at
least 3 per minute to exceed the event-triggering requirement of 2, which is met on the eighteenth sample.
Figure 4 Event trigger
Example 2: Not Triggering an Event
Figure uses the same data to illustrate a case in which a threshold is exceeded without triggering an event.
In this case, the calculated rate of change in the data value is always less than or equal to the high
threshold of 2. At the tenth sample, the rate of change is one per minute. At the fourteenth, twenty-first, and
twenty-fifth sample, the rate of change remains equal to the high threshold of 2. In this case, Fabric Watch
22 Fabric Watch concepts
none ( seconds , minute , hour
minute , Fabric Watch calculates the counter value difference
none , there are two main points to remember when
, or day ), Fabric Watch does not use
minute
is defined. An event