Recently I received an email asking about the difference between Mark Tape as Free and Erase Tape options in DPM. It might be little confusing. But here is my explanation:
You can reuse an expired tape without erasing the contents by using the Mark Tape as Free option. It will overwrite the content. However, you can erase a tape to remove sensitive or critical information by using the Erase Tape option. So if don’t want to erase the tape, you can mark them as free and reuse them. I know erasing the tape process can take hours to complete.
Also, look at the following links for more information:
Mark Tape as Free: http://technet.microsoft.com/en-us/library/bb808995.aspx