Backup control data set size

The BCDS must be large enough to contain the maximum number of records for all the data sets, UNIX files,and volumes that have been backed up.

Figure 1 is an example, based on 3390 DASD, of the BCDS size work sheet. An example calculation follows the work sheet.

To calculate the size of your backup control data set, you need to know the number of backup versions you want to keep and the number of data sets, or UNIX files, that you want to have automatically backed up.

If you are processing UNIX files, you also need to know the number of UNIX files that you will be creating backups for as well as how many unique directories will be visited by DFSMShsm during backup processing. DFSMShsm will create a UFN record to record information about each directory and file encountered. The size of a UFN record is variable based on the absolute path of the file or directory it describes with a maximum length of 1316 (292+length of pathname).

Note: VSAM extended addressability capabilities allow each BCDS cluster to exceed the 4 GB size. In addition, the BCDS can span up to four unique KSDS clusters. For more information about using VSAM extended addressability capabilities, see Using VSAM extended addressability capabilities. For more information about using KSDS clusters, see Using multicluster control data sets.