Foregoing DVDs for Derivatives Backup

Andy,
I personally treat the derivatives just as I do originals - they get put in buckets, and backed up to an off-site drive as well as DVD.

As long as you understand the risks associated with omitting write-once backup, go ahead and do what suits you.

I would suggest, however, that anyone who is going to create a backup system without a write-once component should definitely implement some kind of absolute confirmation regimen. What I mean by this is that you should use something like ImageVerifier on the images (the hash-checking part) so that you can know with certainty that the images have not changed in any way, and that the hardware and filesystems are fully intact.

I'd like to see a day when DVD backup is totally superfluous. I think we're missing some critical information at the moment. My data validation tests have shown lots of invisible corruption on hard drive. Until we get tools that can do easy and comprehensive data validation of all files, it won't be clear if this is just my problem, or if it's widespread. There are some new data validation tools in the new DNG spec that will help throw light on this issue.

I had a conversation with Tom Hogarty from Adobe this week where we discussed this issue. Although he does not advocate DVD as a part of a backup system, he did note that he is seeing an increasing number of corrupted images among users. (These show up with horizontal color blotches in the image area, and don't trigger a error from existing data validation tools.)

Bottom line: Yes, I do suggest write-once media as a part of your archiving system for anything you really want to keep - at least for now.
Peter