Hello,
Media capacity is calculated based upon past experience, once a tape has been read from beginning to end via backups to the tape and then when the tape is overwritten afterwards; or from a long erase or full catalog job.
Hence we request you to perform an erase operation on the tape and check. Also perform a full backup until the tape is filled for example if the tape capacity is 160GB then perform a backup of 160GB with overwrite option. Once the backup is completed and next time when the tape is inserted for backup, check the media capacity displayed.
Hope this helps you.
Regards
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