Thursday, August 19, 2021

Optical Media Durability Update

Three years ago I posted Optical Media Durability and discovered:
Surprisingly, I'm getting good data from CD-Rs more than 14 years old, and from DVD-Rs nearly 12 years old. Your mileage may vary.
Two years ago I repeated the mind-numbing process of feeding 45 disks through the reader and verifying their checksums. A year ago I did it again.

It is time again for this annual chore, and yet again this year I failed to find any errors. Below the fold, the details.

The fields in the table are as follows:
  • Month: The date marked on the media in Sharpie, and verified via the on-disk metadata.
  • Media: The type of media.
  • Good: The number of media with this type and date for which all MD5 checksums were correctly verified.
  • Bad: The number of media with this type and date for which any file failed MD5 verification.
  • Vendor: the vendor name on the media
Surprisingly, with no special storage precautions, generic low-cost media, and consumer drives, I'm getting good data from CD-Rs more than 17 years old, and from DVD-Rs nearly 15 years old. Your mileage may vary. Tune in again next year for another episode.


Bret said...

Back when I used CD-Rs and DVD-Rs, I noticed a lot of them would yellow significantly over time from oxidation (varied with brand, I can't recall which ones). Have you observed any yellowing or oxidation on any of these?

David. said...

No yellowing or visible signs of degradation. They are stored in a cupboard, so in the dark, but no other special storage precautions.

David. said...

One thing I see I failed to mention in the posts is that I always verify the checksums immediately after I write the DVD. Maybe every 6 months or so a DVD ends up in the trash because it fails this test and I have to write a replacement. This happened today.

It might be the case that I'm seeing better longevity than others because they aren't doing this test and rejecting disks with infant mortality.

David. said...

In clearing the garage I found a Memorex CD-R to which I wrote NetBSD's 1.2 release i386 architecture shortly after it was released a quarter-century ago next month. It is 54MB of data. Alas, I didn't write hashes to the CD-R, so I can't fully verify it. But it reads with no errors and the CRC checksums of all the source files are correct. So it looks like I'm getting good data from a 25-year-old CD-R.