Leapdragon 2016 - Aron Hsiao Was Here

DVD-RAM reliability, failures, cartridges, and reading old data.  §

Interesting tech tidbit. Don’t know if it will be useful to anyone.

For a few years between about 2003 and 2008, I used DVD-RAM to archive data of all kinds. I had always adamantly relied on the cartridge-style media because I thought it would protect the discs better for archival purposes.

I eventually switched away because I started to realize that I was having trouble reading from some of the discs, and because it was so damned slow. Put the two together (slow and unreliable), and you have a real PITA on your hands if you need to restore data.

Well, this summer I’ve made a project of trying to get some of the data off of those old discs that is no longer stored elsewhere, and to re-archive it on other media (I now use DLT, though I’ve also thought about switching to LTO—another post in that sometime). It has been a nightmare.

  • Most discs won’t read cleanly. Of about 70 discs, I don’t think I’d had one that read without multiple failures (until today—more on this in a moment). Each time I try to read I disc, I’d get a few files, then some I/O errors, then a bus reset and an eject. And then I have to re-insert the disc and resume the attempt to read it.
  • At times the bus errors cause hangs in system applications (I’m using Mac OS) that can’t be handled with a “kill -9” to the hung processes. The “ps” command shows them either in the “U” or the “E” state, both of which are bad news if they remain that way and a forcible kill won’t work. The Finder process becomes a zombie, the system is beachballed, no keyboard input is accepted, and I have to reset. You can imagine how this multiples the PITA effect of trying to recover data.
  • Some of the discs won’t mount or be recognized at all. I have accumulated a stack of disks with a side marked by a pen-drawn star, indicating that this disc will have to wait until later to try more serious recovery methods.

Because of these issues, it has taken me weeks to plough through about twenty discs. If I get one copied off in a day, I feel like I’ve had a success, and it has to be nursed along continuously with command restarts or system restarts.

— § —

As it turns out, one recent disc wouldn’t mount. So I wrote a star on it and was about to toss it aside when I noticed some plastic sticking out of the cartridge door. I pulled it open and there was some debris still semi-attached to the cartridge, from an improper mold or cut or something like that. I didn’t think much of it because it didn’t come into contact with the disc (it was near the center hole) but just on a lark and in frustration, I broke open the cartridge, removed the DVD-RAM disc, and inserted it into the reader bare.

Voila!

The disc mounted. Not only that, the whole thing (all 4.7GB of that side) copied off without a failure. I’ve now done three sides that way and only had to restart the “cp” command once after I/O errors. That is a significant improvement in readability by removing discs from their cartridges.

— § —

My conclusions?

  1. DVD-RAM is a fundamentally unreliable technology. While data survivability on the media is often specified as fifty years or more, I am getting read errors out of discs that have been in very reasonable storage conditions after just four to five years (note that I did still have a read error after removing discs from their cartridges as well). All of these burns were tested when made.
  2. The cartridges make things worse for some reason. Just why I couldn’t say—the extra weight altering the balance of the internal mechanics somehow? Something to do with airflow? I don’t think it’s friction, as I haven’t heard anything (or seen any scratches) that would support that hypothesis. But the fact remains that discs that wouldn’t mount in-cartridge are mounting just fine out-of-cartridge, and I’ve gone from 20-30 interruptions due to read errors per side to one interruption due to read errors every three sides. That’s a huge improvement.
  3. It’s not just one drive. For backup mechanism reasons I have two Panasonic LF-D211 units and one LF-D311 unit, all purchased at different times and from different suppliers. All have exhibited trouble in reading previously written media over the years. (I originally bought the second drive because I thought the first was failing, then bought the third because I thought the second was failing; then, over the years, I realized that it was just the medium in general that was flaky and each unit was probably behaving according to spec).
  4. It’s not just one brand, age, or capacity of media. I have a mixed bag of Maxell, Verbatim, Imation, OptoDisc, and unbranded cartridge discs with varying case colors and disc colors. They were purchased as needed over the years that I used DVD-RAM. They have all had the same issues, though the 2.6GB-per-side media have performed somewhat better than the 4.7GB-per-side media (again, leading me to suspect some sort of fundamental flaw or tolerance issue in the format).

In short, don’t use DVD-RAM for archival purposes, as they just don’t hold up and writes are unproven, even after verify—and if you have to get a bunch of old data off of DVD-RAM media and are struggling, try busting the discs out of their cartridges, as this seems to radically improve readability for some unknown reason.