The parameter tape_size always defines the physical tape size (tape length * write density). The physical tape size is the total volume (in MB or GB) of the data that can actually be written to a volume without compression. Consequently, different amounts of data can be stored on the same tape size, depending on whether you back up with or without compression. Because BRBACKUP/BRARCHIVE takes this information into account, you never have to or should change the physical tape size if you use software compression or hardware compression (for tape devices with hardware compression).

• If you require several tapes for your database backup, BRBACKUP uses the value of parameter tape_size to distribute the files for backup to the volumes. During serial backups, the program makes sure that the physical end of tape is not reached. During parallel backups, the program also optimizes the file distribution.

• When parameter tape_size is configured too small, the backup program will require more volumes than are actually necessary.

• When parameter tape_size is configured too large, cpio will reach the physical end of tape. See cpio Continuation Tape. In this case, it is essential that you correct the parameter value.

Make sure the parameters required for using hardware compression are set. See for example Tape Devices with Hardware Compression.