Estimating the number of tapes for the backup

Reasons to determine the number of tapes

You should estimate the number of tapes required for the backup before entering the dump command for these reasons:

You can ensure that the dump command does not fail because it runs out of tapes.
You can load the required number of tapes in the tape drives or stackers in advance for an unattended backup. If you do not load enough tapes before entering the dump command and you start the dump command from the console, Data ONTAP prompts you to load additional tapes. But if you start the dump command through a Remote Shell connection, you do not see the prompts from Data ONTAP and the dump command terminates if there are not enough tapes.

To estimate the number of tapes required for the backup, complete the following steps.

Step	Action
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 that needs to be backed up, as described in Determining the amount of backup data.
3	Divide the amount of data by the capacity of a tape.
4	If your estimate indicates that your data will nearly fill the last tape, add a tape to the estimate in case the backup exceeds your estimate. This is especially important when using compression, because compression rates vary based on the data.