DPM will verify whether the selected items can be read from the tape that contain them. Readability of data in a tape is ...

DPM will verify whether  the selected items can be read from the 
tape that contain them. Readability of data in a tape is a good 
indication that those data could be recovered as well.

You would be able to monitor the progress of verification in Jobs
tab of Monitoring task area.

Click on OK to start the verification.

            The tapes containing the selected items are offline. You can
            trigger the verification job now and add the tapes in the
            library in next 1 hour.