However, the propsect of ever losing nearly five gigs-worth of images or data is just awful and we're writing two copies of each DVD at present and I intend to check a sample every three months to make sure I can read files on them.
I'm pretty much in the same situation and have experienced the same successes as you.
In my early go with DVD I experienced panic about multiple big disks of archived data when I realized that numerous disks that were burned and verified without a problem in Toast were in fact not fully readable. It turned out to be a media format problem. I had recorded everything on DVD+R disks as that's what works best and is recommended for the drive that I use with Retrospect. Macs as a VERY broad generalization are more DVD-R friendly. PCs more DVD+R friendly. The disks would mount and could be at least partially read from the internal DVD-ROM in my G4. That's why I never detected a problem early on. But try to copy an entire disk; or move a large chunk of data off of it and it would almost certainly give errors. The disks would not mount or be recognized at all in the drive (external Sony) that created them. Of course I discovered all of this AFTER trashing the original data because I thought I had multiple copies backed up to DVDs. The same disks that looked problematic on my Mac (which created them) would read perfectly on a Windows system. At that time I wasn't running Windows in my office except for Virtual PC. Using Virtual PC, the same drive that wouldn't recognize the disk under OS-X (which using Toast created the discs) would now read the discs just fine. I copied all of the data through Virtual PC back to the Mac hard drive. Talk about watching paint dry... an insanely slow process. Once back on the Mac I reburned the disks onto DVD-R media and now have disks that read just fine in any of my Mac DVD drives.
All of the above didn't do anything to add to the confidence of my archiving scheme, but the volume that I'm archiving these days dictates that something more than CD is needed. I think the most prudent course of action besides making at least two copies of a disk is to put it on two different brands of media. If one proves problematic and short lived, its likely the other will have different (hopefully better) results. In the case of DVD, if you have appropriate drives, it may be worth putting one copy on +R media and one on -R media to insure future compatibility with an assortment of drives.
No matter what you use its pretty much a given that over some period of time you're going to want to move from that media to whatever the latest most efficient media is. I've moved much of the data I have on old DAT tapes going back to '93 to CD. I've now moved some of my larger CD archives to DVD for the convenience of having a larger pile of related images on one disk. Of course the original tapes and CDs are kept as well so there's even more redundancy available. By the way, I've yet to encounter any problem pulling data off of even some my oldest DAT tapes...and this is supposedly one of the most fragile types of archive.
Bob Smith
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