Defining the number of OLDSs

You must define at least three OLDSs (or OLDS pairs) to start IMS. However, you can define additional OLDSs (up to 100).

You must define the OLDSs to be used during initialization in the IMS.PROCLIB data set using the OLDSDEF statement. You can then dynamically allocate additional OLDSs. Specify the OLDSs you want to dynamically allocate using the DFSMDA macro; later you can use the /START OLDS command to add an OLDS.

Related reading:  For more information on the DFSMDA macro, see IMS Version 15.5 System Definition.

When deciding how many OLDSs to define, consider the frequency of archiving and the amount of data you want to keep online. IMS reuses an OLDS only after IMS archives it. The number of OLDSs you define should be consistent with the frequency of archiving; if, for example, you archive frequently, you can probably plan on defining fewer OLDSs.