Poor sales hurt disk's availability

Q: Why aren't there any rewriteable double-layer DVDs? I can find dual-layer disks only in write-once formats that I can't reuse.

Recordable DVDs can hold 4.7 gigabytes of data, and once that must have seemed like an inexhaustible capacity. But now that one year's worth of digital photos can max out a disk, the 8.5 GB allowed by “dual-layer” disks looks a lot more attractive.

But as the questioner noted in a recent Web chat, the only dual-layer discs for sale are write-once blanks, not the more useful rewriteable kind.

That's not because DVD technology prohibits such a thing. A few years ago, the DVD Forum, which sets industry standards, approved a set of specifications for dual-layer rewriteable DVD-RW media, and the same work has been done for the competing DVD+RW format.

But other factors hold back these higher-capacity rewriteable disks – starting with high prices and limited compatibility, said Hugh Bennett, an industry consultant in London, Ontario. He said that dual-layer rewriteable disks are expensive and inefficient to make and that they don't work in existing DVD players and drives.

Andy Marken, a spokesman for the disk vendor Verbatim, also pointed to the historically poor sales of rewriteable disks, noting that sales of write-once CDs and DVDs have outpaced those of rewriteable disks by a factor of five. That gives manufacturers little incentive to make dual-layer DVD-RW or DVD+RW formats work.

So how are you supposed to back up all of your photos? The best high-capacity backup tool remains an external hard drive that you can plug into any other machine – although it's a good idea to keep a second backup of your most important files on a DVD or six.