Too bad at the momnent the best durable way to store data is the stone (pyramids are still there after thousands of years ;))
Optical discs are not totally unreliable however. If you buy quality discs like Verbatim or Taiyo Yuden, you can save your data safely for many years
Even hard disks are not the most reliable data storage solution, because with the time also these devices can become damaged.
If you can copy all files from the disc on a HDD, however, any data will be not degraded in any way.
The best solution to safely store your data then is to make multiple copies in different supports. So if you can afford it I suggest to buy some hard disks and a bunch of quality discs (avoid [B]rewritable[/B] media because as I said these are not fully reliable), and then make multiple copies of your data