Defining VSAM data sets
The Monitor III data gatherer writes records (sets of samples) to a large storage buffer, or optionally, to user-defined VSAM data sets. Without the VSAM data sets, the data is overwritten as soon as the buffer is filled. If you define VSAM data sets, you can save large amounts of information, and you can reuse the VSAM data sets as RMF™ continuously records data over time.
You can define up to 100 data sets for use with the data gatherer.
You should define at least two data sets, because the gatherer deletes
all data in a data set before writing to it, so a single data set
would be emptied immediately after it was filled. RMF can keep about 1100 sets of samples in one data
set. Based on practical experience, we recommend to define six VSAM
data sets, each with 50 cylinders disk space. On small and medium
systems, this will allow for about two days of data.
Note: If
you need to change the amount of space later to meet your installation's
needs, we recommend adding more data sets, but not making the individual
data sets larger. Increasing the size of the data sets may cause RMF to run out of index entries and
be unable to fill the additional space.
Have a look at the Data Index (see Using the Data Index (DI)) which tells you exactly the time range of the data that is available in your VSAM data sets. This can help you in defining the appropriate number of data sets.