Since everyone has chimed in with a tech solution, let me offer a business solution:
Have you determined that you actually need this 500TB of media? If you're not using the data every day, do you really need it? A lot of businesses hoard data without ever analyzing why or if they should keep it. Keeping data for records retention laws is one thing, but keeping data just because you have it is a poor business decision.
After running a thorough analysis you might determine that you only need to keep 100TB or so.
We definitely have orphaned data in the mix and are working to purge it. However, most of the data has to be kept in case its needed in the future (however unlikely that may be).
Have you determined that you actually need this 500TB of media? If you're not using the data every day, do you really need it? A lot of businesses hoard data without ever analyzing why or if they should keep it. Keeping data for records retention laws is one thing, but keeping data just because you have it is a poor business decision.
After running a thorough analysis you might determine that you only need to keep 100TB or so.