Microsoft Knowledge Base Article 265487 contains the following summary:
Using Remote Storage (RSS), you can create up to three media copies of master media (tape). The master media houses files that you want to move from local hard drive storage to remote storage thereby using less of the expensive tape media. If you have media copies, you prevent having a single point of failure should the master media get lost or damaged.
Creating media copies require two basic steps, specifying how many copies are desired, followed by running the Synchronize Media Copies wizard. You can view more detailed steps in Remote Storage Help.
NOTE: Run only one media copy job at a time to ensure that the master media and tape drive resources are available to complete the task. Multiple media copy operations cannot be run concurrently.