Calculating DASD space for the journal

Table 1 helps you to calculate DASD space requirements for the journal. To determine the number of resources in your library, such as the number of scratch mounts that you have, see your answers to Evaluating removable media management needs. Base these calculations on your requirements from one backup to the next. To ensure that the journal has enough space when there is an unexpected increase in tape activity, increase the calculated amount by 50% or more. The journal size can exceed 65 535 tracks.

Table 1. DFSMSrmm journal DASD space requirements
Journal Content	DASD Space
Changes by users	1.5 KB for each change made
Data sets	1.5 KB for each data set retained by a vital record specification
Data sets no longer retained by a vital record specification	1.5 KB for each data set no longer retained by a vital record specification
Expiring volumes	1.5 KB for each expiring volume
Non-scratch mounts	6.7 KB for each mount
Scratch mounts	8.3 KB for each mount
Volumes	1.5 KB for each volume retained by a vital record specification
Volume checked in/out	2.6 KB for each volume in or out of the library
Volumes returned to scratch	3.0 KB for each volume returned to scratch
Volumes to and from storage locations	3.5 KB for each volume moved to or from a storage location
Volumes no longer retained by a vital record specification	1.5 KB for each volume that has not reached its expiration date and is no longer retained by a vital record specification
Volumes that are exported or imported	1.5 KB for each logical volume exported or imported
Vital record specifications	1.3 KB for each vital record specification created

Convert the final figure into a space allocation. The journal has a record format of variable-length blocked records. You do not need to specify the record format information when allocating the journal, because DFSMSrmm sets the correct values when it opens the journal data set.

To calculate the space required, divide the total KB of space by 4, as allocation will be by average record size using a 4 K value. This calculation gives you the number to use in the space allocation (SPACE=) shown in Figure 1.

On test and recovery systems where you plan to use the JRNLTRAN(YES) function, increase your estimated journal size by 33% to allow for the extra journal records that are created.