Calculating DASD space for the DFSMSrmm control data set

Table 1 helps you to calculate DASD space requirements for the DFSMSrmm control data set. To determine the number of resources in the library, such as the number of software products you have, see your answers to Evaluating removable media management needs.

Table 1. DFSMSrmm control data set DASD space requirements
Control Data Set Content	DASD Space
Control record	1 MB (MB equals approximately 1 000 000 bytes)
Data sets	512 KB for every 1000 data sets
Shelf locations in the library that do not contain volumes	140 KB for every 1000 shelf locations
Shelf locations in storage locations	140 KB for every 1000 shelf locations
Owners	38 KB per 1000 volumes
Software products, average five volumes per product	420 KB for every 1000 software products
Volumes	1 MB for every 1000 volumes
Vital record specifications	212 KB for every 1000 vital record specifications

After calculating the previous figures, increase the total by approximately 50% for free space in the VSAM key-sequenced data set. For example, if the calculated size is 3000 KB, increase it by 50% to 4500 KB to allow for free space. Also consider your expected future growth in numbers of tape volumes and data sets, such as acquiring a new virtual tape solution, and build this expected growth into your size calculations. Use this calculated value in the access method services KILOBYTES parameter on the DEFINE CLUSTER command shown in Figure 1. See Monitoring the space used by the control data set for information about monitoring the DFSMSrmm control data set space usage.

The size of the records in the DFSMSrmm control data set is variable, and record sizes increase as new function is added. Thus, the space required for your DFSMSrmm control data set increases over time. For example, each time a volume record is updated, such as during inventory management or when a new data set is written on a volume, the associated control data set volume records change in size or increase in size as they migrate to the new level dynamically. The value you use for free space enables DFSMSrmm and VSAM to handle the record size changes and allows you the ability to easily add new resources to DFSMSrmm at any time. Because of the way that DFSMSrmm handles variable length records, it is recommended that you do not use FREESPACE(0 0) when defining the DFSMSrmm control data set.