Erasing tapes is always a time-consuming process, and this is a very common scenario regardless of the product, as the tape will be formatted. A faster way is to perform a short erase.

Enter the DWORD UseShortErase in the registry on the DPM server and reboot the server:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft Data Protection Manager\Agent

Provide the value of 00000000 in a DWORD.

Short erase means that the data written to tapes will be overwritten with a NULL value that makes it appear empty

For a tape to be erased, it must not contain any recovery points that are within the retention time.