6. DATA SOURCES › 6.6 Notes on RMF Samples

6.6 Notes on RMF Samples

Many statistics are recorded by RMF in the form of a count of
samples when a particular condition is true.  The total
number of samples taken are used to calculate averages and
percentages based on these sample count statistics.

For example, to gather statistics about input/output devices,
RMF periodically scans each Unit Control Block (UCB) of
eligible I/O devices to determine the state of each one.
Along with other indicators, there is a bit indicator
(UCBALOC) in the UCB which, when set, indicates that the
device is currently allocated.  RMF then reports the number
of times when this bit was set during the measurement
interval in field SMF74ALC of the Device Activity Record.
The total number of times that samples were taken from field
SMF74ALC must be known to determine the percentage of time
when a particular device was allocated by using the following
formula:

                DVAPCALC=(DVAALC*100)/DVARSMP;

Where

    DVAPCALC = Percent Device Allocated
    DVAALC   = Number of Samples When UCBALOC Was Set
    DVARSMP  = Total Number of Samples Taken During the
               Measurement Interval

The following sections detail the various issues associated
with RMF samples counts:

    1 - Names and Presence of RMF Sample Count Elements
    2 - Skipped Samples
    3 - Number of Samples and Statistical Validity
    4 - Sample Count Differences and Merging Files