DVDs can be a good way to archive data. Using more than one hard drive is good, but DVDs have some advantages. If you drop a hard drive, you will probably lose everything. DVDs can be easily kept at multiple locations. That's what mothers are for, you know.
But to get reliable DVD storage, you have to know how to get good burns, and like always, you need to make more than one. I don't generate much valuable data, so a DVD backup of all important stuff once a month or two is adequate. If last month's DVDs should somehow be lost, I wouldn't lose much by using an earlier one.
To make good DVD burns you need to get good blank DVDs. You can't necessarily tell what media you have by looking at the label. Some media give bad burns, with lots of correctable errors, and some media can make good burns today, but 6 months from now they may be unreadable. These discs may be readable today in your current drive but might not be readable tomorrow, or in a different drive.
To know what discs you have, you need to see the MID (manufacturer's ID) that is recorded on the disc. The
CD-DVD speed program (usually called CDspeed) will show you that. People that have thousands of DVDs and are particular about them agree that the MCC MIDs (Mitsubishi Chemical Corp.) and the MIDs used by Taiyo Yuden are the best. Most +R and -R discs sold by Verbatim have a MCC MID. To get Taiyo Yuden you can buy them at rima.com
Then you have to scan the burned disks. Just reading them back is better than nothing, but that just tells you they are readable today in that optical drive. There are tests that can give you more confidence that the disks will be readable in other readers and readable in the future.
The CDspeed program has two tests for this. The Transfer Rate Test can be run on any DVD drive. This test attempts to read the disc at full speed, and plots the speed during the read. Any dips in the graph indicate the drive slowed down because it encountered excessive correctable errors. Well, if your CPU is busy or you have a bad connection to the drive, that will cause dips also.
The Disc Quality test can only be run on drives that can report the number of errors it encounters. The disc is read at a constant speed and the errors per block are shown on a graph. All discs have errors (correctable errors). The difference between a good disc and a bad disc is the number of errors.
You can learn about this and more at cdfreaks.com