There are some CD-R's that are sold as "archival" and more expensive as well. May be worth investing. It is indeed wise to make two copies. They would be best stored in different places.
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Just plain wrong. Mitsui CD-R discs ( http://www.mitsuicdr.com/ ) are certified for 100 years (300 years for their gold discs). That means their actual data integrity is rated for that long, not just a guarantee that Mitsui will replace the CD if it fails (which of course is worthless because the data cannot be replaced).
As others have suggested, use top quality CDs, make multiple copies and store sets of copies in different physical locations. People do loose their pictures to fire, theft, etc. Digital gives you a clear advantage here.
And use different CD manufacturers. There is always the possibility that a given batch of CDs may have problems, and even if the manufacturer is still around, the most you will recover is the cost of a CD-R (what about $0.10 in todays market).
You also have to plan on media obsolessence, and budget for copying the files every 5 years or so as new media comes out. How many people still have 8" floppy drives on their computer or 8 track tape deck players in their cars?
On the other hand, whether the current CD/DVD format will be with us for 100 years is a different question. I think in 20 years (probably much sooner, say 5-10 years), kids will look at people who recall CDs with the same scorn as kids do now for people with vinyl records. Certainly in terms of music formats, I've seen 8 track, cassettes, 78 RPM records, 45 RPM records, 33 RPM LPs, CD, DVD, blue lasar DVD, DAT, etc. In terms of tape storage, I've used 800/1600/6250 DPI reel-to-real, DAT DDS 1/2/3, and I currently use AIT tapes, and there are a couple of other formats I haven't used. In terms of disk connections, I've seen 5 versions of SCSI, a couple of IDE versions, USB 1.1, USB 2.0, firewire, etc. Change occurs, and you can either plan for the change, or get wacked over the head when it comes.
It depends on the storage conditions and the tape. Also for daily backups, I found HP DAT drives lasted about 9 months before they wore out (doing 5 hours of dump and verify every night). If you only use the tape weekly or monthly it will prolong the life. DLT's are supposed to be more reliable (and expensive).
There's a BIG difference bewteen predictions and fact!
The only way to have factual longevity data is to actually wait centuries and see if the CDs hold up. Feel free to get started on those tests, and let us know how they turn out.
