Is the geometry of data on burnable media deterministic?

Question

Is it possible to determine the physical location (e.g. angle + radius) for a particular bit on a CD/DVD/BluRay disk?

The reason I'm asking is this, I want to design a data structure which stores recovery information approximately on the opposite side of the medium to avoid a single scratch from making the whole exercise moot.

Klee

Interesting idea. I've no real knowledge, but are you sure that any of the core data structures that put a file system on a disk are suitably redundant also? E.g. there's no point in this data being safe from a scratch if the entire disk can't be mounted because of a scratch on a critical part of the disk. – Worl

That's easy, when it happens you have the tool to read the medium directly and find the data you need. Something akin to fsck with output to disk. – Klee

It's certainly possible to determine where particular bits will be written on the disk, but you'll almost certainly have to lay out the data yourself rather than letting some existing burner software do it for you. Doing so is more complicated if you want to support ISO-9660 and derivatives, but still possible. And if you want to support recovery, you'll have to write your own low-level driver that can access the thing without it being mounted (because a scratch could make the file system unreadable). – Cox

@JimMischel ... do you know how it can be done? The standardized formats should be sufficient. – Klee

Answer 1

CD/DVD/BlueRay encoding schemes include code correction. This is basically another layer of data redundancy which allows the algorithm that decodes the disk to be able to not only detect errors but fix them. When the original engineers and computer scientists decided the encoding schemes for these disks they took scratch resistance into account.

See Reed Solomon codes which are used on CDs/DVDs/BluRay Disks

Beane

Doesn't answer the question at all. – Klee

I'm just letting you know that what you are trying to do might not be worthwhile as DVDs/CDs/BluRay already have this scratch protection. – Beane

Well, you didn't state it explicitly in your post. Anyhoo, the ECC on DVDs works decently, but statistically after MANY backup DVDs burned and stored and moved around for a decade, some sectors are lost (and that's with everything burned in duplicate). So I want to see what I can find out about the layout of the medium to store additional recovery data in the future. The story is long and the details are irrelevant. The key part is, a real answer would be of specific benefit. Anyway, thanks for your time. – Klee