It's "zero bytes" because you don't have permission to enter the directory. However, if System Restore is turned off, there are just a trivial amount of files in there (just one I think but I can't remember for sure). tracking.log

To grant your username access so you can verify that there are no disconnected files piled up in there:

cacls "driveletter:\System Volume Information" /E /G username:F

To remove access afterwards:

cacls "driveletter:\System Volume Information" /E /R username

I do recommend checking, especially if you have inexplicable storage discrepancies, because I've seen that directory as large as 25 Gb when files don't get deleted when something goes wrong with the tracking mechanism for whatever reason. (One example... I suspect dirty reinstalls of XP where someone just keeps saying yes and lets it delete the contents of the Windows directory. All the System Restore crap from the previous installs is disconnected and must be physically deleted after turning it off)