Use Table 1 to determine the estimated capacity of an IBM cartridge tape when OAM is storing either objects or the backup copies of objects on IBM cartridge tape written on IBM tape subsystems.
If the object being stored is relatively small (16 KB or less), then the capacity of the tape cartridge can be substantially reduced. Likewise, if the size of the object being stored on tape cartridges is large, the capacity of the tape cartridge can be increased and better used. The smaller the object size, the more buffer space is required to separate the objects.
For example, if the data on an Enterprise Tape Cartridge 3592 compacts at a 3 to 1 ratio, the tape (on a 3592 Model J) can store as much as 900 GB (using EFMT1).
Recommendation: The tape compaction capability provides hardware compaction in the tape control unit and can increase the effective capacity of the tape media. Enable the compaction feature when OAM is writing primary copies or backup copies of objects to tape.
If the data that OAM is storing already is compacted, you should not expect any increase in the effective capacity of a tape cartridge due to the use of compaction. This situation is true for image data (such as ImagePlus® algorithm suited for image data). In addition, if the application invoking OAM for storing data is compacting the data, such as with the Item Access Facility (IAF) program, you should not expect an increase in the effective capacity of a tape cartridge using compaction.
OAM provides the capability for each Object or Object Backup storage group to specify what percent full OAM is to fill each tape cartridge belonging to the storage group. This option is specified with the TAPEPERCENTFULL keyword on the SETOAM statement in the CBROAMxx PARMLIB member.
Recommendation: If you want OAM to fill the tape cartridges to a certain percentage of their estimated capacity, reduce the approximate capacities listed in Table 1. If your installation specifies the tape volumes should be filled to 90% of the estimated capacity, reduce the approximate capacities listed in the prior table by 10%.