home | list info | list archive | date index | thread index

Re: [OCLUG-Tech] cd burning problems



I am now  assuming the problem is with the CD burner
and that it needs replacing.

A 50% failure rate is not uncommon with blank media that you buy in the store.

No CD ever burns perfectly: the expected error rate is between 1:10000 and 1:100000. There are then three levels of error correction applied: Cross-Interleaved Reed-Solomon Coding turns 24 bytes into 32 bytes. Then it's encoded on disc using 8 to 14 modulation. These two processes produce an error rate acceptable for CD's, but not for CD-ROMS. CD-ROMS add a third level, the Reed-Solomon product code, which turns 2048 bytes into 2366 bytes.

In the end, only 28% of the bits on the CD-ROM are actually data, the rest is error correction, with a few left over for synchronization.

The whole point is that the format is designed to work with pretty poor media. So that's what they sell you, because it's a heck of a lot cheaper than the good stuff.

Follow one of these three rules when buying media:

1) "made in Japan" in the fine print.  The brand name is meaningless.
2) Taiyo Yuden.
3) Verbatim. They may relabel products from other makers, but at least they appear to do it with integrity (with one notable exception).

If you can't get one of the above three, you can try Ritek. They aren't a "tier-1" manufacturer, but at least they're putting their own name on their own product.

Pretty much every other "big name" (Sony, Imation, Maxell, etc.) very commonly resells crappy CDs/DVDs under their own name. If they made it themselves, it's probably OK, but if they didn't, who knows?

Once you burn it to CD, you can do a "readcd -c2scan" on the media. This tells you how many errors were corrected by the third level of error correction, and gives you an idea how good the CD is. Most unscratched "pressed" CD's will give a 0 value, but few CD-R's will. That's OK, error correction is there for a reason. But if the number is high, you wouldn't want to trust the CD for important data.

On a DVD, the equivalent is a PI/PO scan. Unfortunately, I'm not aware of any tools in Linux to do this scan.

sources:  wikipedia and http://www.digitalfaq.com/media/dvdmedia.htm

Bryan

references