Oracle RMAN Pocket Reference

Media Management Layer

The Media Management Layer (MML) is a third-party piece of software that manages the reading and writing of files to and from tape. An MML also keeps track of which files have been written to which tapes. If you want to back up your database files to tape, RMAN requires you to use an MML. If you plan to use RMAN to back up files only to disk, you do not need an MML.

MML tools are often used by System Administrators to back up the host O/S filesystems. If your work environment already uses a MML, you can leverage this architecture to implement RMAN backups to tape. There are several reasons to back up files to tape and thus require an MML:

• The expense of storing large backups on disk is too costly.

• Your requirement is to back up files somewhere other than on the same server as the target database, thus reducing your risk of losing both the target database and backup files at the same time

When backing up files to tape, an MML keeps track of which files were written to which tapes. In the event that restoration of a database file is required, RMAN communicates to the MML a list of the backup files that are required to restore the database file. The MML then determines which tapes contain the required backup files, retrieves the requested backup files, and passes them back to RMAN; RMAN then restores the database file.

Setting up RMAN to work with an MML can be the most frustrating and difficult part of implementing RMAN. This is because determining the root cause ...