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Estimating the number of tapes for the backup

You must estimate the number of tapes required for the backup before executing the dump command. This estimate helps you to ensure that the dump command does not fail because it runs out of tapes. It also helps you to load the required number of tapes in the tape drives or libraries in advance for an unattended backup.

About this task

If you initiate the dump command from the console and have not loaded enough tapes, Data ONTAP prompts you to load additional tapes. However, if you initiate the dump command from a Remote Shell connection and have not loaded enough tapes, you do not see the prompts from Data ONTAP and the dump command terminates.


  1. Determine the capacity of the tape device you are using for the backup by entering the following command:
    sysconfig -t
  2. Determine the amount of data to be backed up.
  3. Divide the amount of data by the capacity of the tape.
  4. If your estimate indicates that your data will nearly fill the last tape, add a tape to the estimate.

    This avoids a backup failure if the backup exceeds your estimate. This is especially important when using compression, because compression rates vary based on the data.