SuperDrive - one in five dvds won't mount I recently turned my 2009 mac mini into a mediacenter. 
It appears that about one in five of my dvds will not even mount. I suppose this has to do with some copy protection. Same goes for my music CDs.

I would be willing to buy an external drive - but I'm worried that in the end it will have the same issue (and I won't be able return a "functional" drive). And so far I don't know which "feature" will be required to play all DVDs.

Web search only gave me info on failing drives that won't read any media. But as I can reliably read some media I don't think these apply to my case.

I hope someone can shed some light on this issue.

Some additional info

About the mac mini - in the course of turning it into a media center I did a fresh install of mountain lion with latest updates. The only additional software installed is XBMC and VLC. So I doubt this might be a software issue.

Before that I hardly used the drive. I think I only used it like a dozen times. Also didn't burn any disk.

DVDs won't open in the Mac DVD player software and not even mount as data disc.
It would be good to know if the one in five is the same disk each time, or if it's more a case of roughly every 5 attempts the mount fails.  If it's the same discs everytime, then you could further troubleshoot by trying them in other devices.  If it's random discs, then it's likely your drive that needs troubleshooting.

Does it make any weird grinding noises, or excessive head seek operations before giving up on mounting?  And does it sometimes fail to eject the drive if it has failed to mount?  I ask because this is exactly what my iMac superdrive (2009 era) did.  Sometimes it would read, sometimes if would make awful noises, sometimes it wouldn't eject because it said there was no disc when there was.

I eventually removed it and replaced it with an SSD instead, and for the price of a few dollars on eBay I bought an external USB case for it to see if I could get it working at all - it's worked fine ever since!  Maybe just being rough with it and being able to shake it about and stuff when I removed it (in a way I couldn't so when it was internal to the iMac) helped?

If it is the drive, you have limited repair options other than percussive maintenance, a monster clean with a vacumm nozzle right down the slots, and re-seating the cables etc.  You could try putting your Mac Mini on it's side when inserting discs - sounds daft, but I've know this to work with failing drives.

As for replacing it, then any DVD drive is going to be absolutely fine if you just want to read discs.  Frankly you will struggle get a DVD-ROM, and anything you buy will be a writer also, but there is no need to go for the fancy options like dual layer burning, lightscribe lazer etching, Blu Ray playback etc etc.