There is one tool that I have previously used and have seen used by other companies, and that is StorSentry.
It is writtemn by a company in France called Hi-Stor ...
http://www.hi-stor.com/site/index.php?pge=62
... and marketed by Imation
http://www.imation.ae/storsentry/index.html
Without going into too much detail, I've used it, I've seen it used and it does exactly what it says on the tin.
There is a cost, but given there is no need to replace media until StorSentry tells you to there is a saving made on not having to replace your're media every x years.
Typically, for a company that replaces 100% of the media every 3 yeras, the Storsentry product would, if installed, pay itself back after 3 years, and return a saving thereafter.