Once, in the early days, we had Macs with SCSI connectors (SCSI - does anyone remember?) and some external hard drives (with the unbelievable storage capacity of 2 GB). Then the first Macs with FireWire only showed up -- in some nights all files had to be copied (...passing hours in the sandglass) and over the time the SCSI drives were sold or simply thrown away because it was to expensive to buy/establish/maintain a separate communication channel with old-fashioned SCSI drives. After discovering that some files hadn´t been copied properly, it was too late... . Two or three years later the last removable SCSI hard drives (Syquest 44/88MB, Iomega 1 GB) refused to work.
Now, there had been a lot of research going on in the last years how long and under which circumstances CDs and DVDs probably could live longer than three or five years. David is quoting the results of a examination called "Digital Media Life Expectancy and Care" by Michael W. Gilbert, last revised thursday, 12 June, 2003:
"With moderate care, most magnetic media will last for 10 years. With special storage and handling, digital magnetic tape formats can reliably store information for 30 years or more."
Not to be misunderstood: we are not talking of saving the files of a company (datacenter, RAID, multi location distributed files etc.), but the problem how a private person might handle all those files... and not only until the next generation of macs or pc shows up in the rooms of your preferred local dealer.
To outline the problem: if you burn -- as a backup of your hard drive --about 120 CDs/year (10 CDs/month) to store some of your images, you will have to reburn all those files at least five years later to be on the secure side (about 78 GB). These are only the files of one short year... . Good night and farewell my lovely if you only have one built-one hard drive for recovering purposes...if your drive crashes, you´ll have to insert hundreds of CDs manually...if they still word after 5 hot and humid summers.
So the only solution for a private person can be (besides RAID): a second built-in drive for backup-only, two external hard drives (capacity > 250 GB; three might make more sense), and t h e n CDs/DVDs.
By the way:
Life expectancy of photographics slides: 100 years. Egyptian stone tablet: 2,200 years. And: a thief might steal your mac/pc, your hard drives - but never your slides.