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How To Choose Archival CD/DVD Media
An anonymous reader tips us to an article by Patrick McFarland, the well-known Free Software Magazine author, going into great detail on CD/DVD media. McFarland covers the history of these media from CDs through recordable DVDs, explaining the various formats and their strengths and drawbacks. The heart of the article is an essay on the DVD-R vs. DVD+R recording standards, leading to McFarland's recommendation for which media he buys for archival storage. Spoiler: it's Taiyo Yuden DVD+R all the way. From the article: "Unlike pressed CDs/DVDs, 'burnt' CDs/DVDs can eventually 'fade,' due to five things that affect the quality of CD media: sealing method, reflective layer, organic dye makeup, where it was manufactured, and your storage practices (please keep all media out of direct sunlight, in a nice cool dry dark place, in acid-free plastic containers; this will triple the lifetime of any media)."
How apropos.
'slashdotters' can eventually fade due to five things that affect the quality of slashdot comments:
Have you read my journal today?
"(please keep all media out of direct sunlight, in a nice cool dry dark place, in acid-free plastic containers; this will triple the lifetime of any media)." And NEVER ever feed them after midnight. On a more serious note, I used to worry about eventual degradation but it's coming up on 10 years that I've owned a CD-R drive and I have yet to run across a burned CD I cannot read due to this sort of degradation. Maybe at the decade mark, some of my discs will fail me and I'll change my mind but right now I'm not too concerned.
direct sunlight in your parents basement. ;)
Repeating again and again and again:
For backups and archival you need tape backups, stored offsite. If you want something with more capacity and faster recovery, a backup server with rsync and beefy hard drives. Nothing else will do. With the time and effort you'll spend searching and writing DVD media you could have already bought and set up a file server or bought that tape drive.
Unless you're going to be taking those backups with you and using them in high volume, backing up to DVDs is simply a waste of time and space, and when you get some dreaded CRC errors you'll be crying for not having done otherwise.
sig: Cosas varias de un sysadmin argentino: http://aosinski.phpnet.us/
I now have some no-name-brand CDs burned in 1998 that are still good. I have never had a good, name-brand CD fail for any reason. The only failure I have ever had was the top layer peeling off some el-cheapo CDs which were stored in plastic sleeves, not jewel cases. One BIG key the article does not mention is to store the disc where the burned surface is not touching anything, such as in a jewel case -- the article should have mentioned that. Do not put in plastic sleeves or cases with slide-in sleeves. Odd that the article is a sales pitch for that T-Y brand -- what about RiData? That's what I use for DVD archival storage. I haven't been using DVD-R long enough to comment on how long they'll last. I have always found the alarmist idea that CDs will spontaneously self-destruct to be sort of over-the-top. CDs seem much more reliable for archiving than any other medium like diskette, hard disk, USB flash, or tape. Flash is more reliable, but has to be refreshed or it will disappear.
Why not just get a NAS that has RAID? That would make more sense. When a disc dies, you can replace it, rebuild your array, and everything is fine. PLUS, you could expand your archive over time.
I think it's absolutely stupid to use a DVD jukebox. Really. Look into a NAS box with RAID.
It's either on the beat or off the beat, it's that easy.
I moderate therefore I rule!
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Some Verbatim DVD+Rs are manufactured by Taiyo Yuden. Strangely, the ones I used were the cheap-looking colored ones, but I've used several batches of those with excellent results. Speaking of Verbatim, some of their other discs are made by Mitsubishi, and those also very good, although I'm not sure how they'd work for PS2 piracy ;)
I've seen Taiyo Yuden CD-Rs and DVD+/-Rs in a number of retail stores under various brand names. I'm hesitant to publicize my trick, but I suppose the Slashdot community should know. Here's how to spot Taiyo Yudens quickly in the store, without checking each label for "Made in Japan":
The spindles all have a unique bottom lip. Whereas most plastic spindle coverings are the same diameter from the top of the spindle to the bottom, Taiyo Yuden cases have a "lip" on the bottom of the plastic covering that starts about an inch from the bottom. The bottom of the clear plastic covering sticks out just a bit and then recesses to the diameter of the rest of the spindle. Taiyo Yudens comes in these cases no matter how they are branded, and I have never seen a spindle of discs with this bottom lip that are not Taiyo Yuden. I guess Taiyo Yuden supplies the plastic spindles as well as the branding on top of the disc.
In any case, I have had better luck with the consistency of Taiyo Yudens than any other brand of DVD+R. I'm not sure what the case is now, since I've only been using Taiyo Yudens for the past few years, but when DVD recording was first becoming affordable, the compatibility of much DVD media with various recorders was so terrible as to be useless (and endlessly frustrating). Taiyo Yuden makes quality discs, and it's always nice to spot them in the store when there's a deal going on.
Oh, I'm so tired of these articles. Everyone concentrates on dye fading, because I guess it's easy to measure and quantify. If dye fading were the failure mechanism for these disks, they'd last twenty to two hundred years... according to vendors and researchers.
Everyone says "I've never had any trouble with brand ABC," but the thing is, ABC varies depending on what you read or who you talk to. Some people insist they've never had any trouble with the cheapest generic products they buy at Staples. Some say any name brand is OK. Some say Verbatim is good. Some say to stay away from Verbatim. The more sophisticated will tell you not to use anything but phtalocy- pthalocy- pffthal- the Mitsui stuff. Others (like this guy) are partial to other dyes. Some say you're a fool to use anything but Mitsui Gold... some say they're an overpriced waste of money.
It's all authoritative sounding talk, talk, talk and no two experts say the same thing.
In reality, I don't think anyone understands very well what actually causes these disks to fail in the real world. I've had disks fail in less than two years--maybe only a couple-three in many hundreds, but certainly not zero--and I've never seen any obvious pattern as to which of them fail.
The thing that really bothers me is that drives and/or their accompanying software drivers never give you any indication of what the signal quality of a particular disk is. If they did, you could detect that a disk was deteriorating before it failed, and make a copy. As it is, they just keep silently keep correcting errors behind your back and you have no warning until there is utter, catastrophic failure.
"How to Do Nothing," kids activities, back in print!
I'm surprised to hear that consumer media can last so long. I was under the impression that consumer media would only last at most 20 years. Good to know it is longer.
All current forms of optical storage share the same problem that will limit their reliable life span. This problem will effect different media design types over different periods of time, but 20 years is a good average before you will start to see bit rot. How ever ALL optical media, regardless of being commercialy pressed or being consumer grade CD/DVD-R, will eventualy suffer bit rot for the exact same reasons. The problem is that the rate of expansion and contraction of the metal substrates that make up the innner layers and the plastics that make up the outter layers are very different. All optical media will suffer bit rot over time because of this, as what eventualy happens is the metal substrate inside the plastic protective layers gets warped and ripples start to form in the surface. This of course starts to alter the smooth/pit reflection encoding of data on the disc and ruins the data.
Again, different types of optical media design will last longer than others. Yes, commercialy pressed CD/DVDs will last longer than consumer grade CD/DVD-R media on average. How ever none of these formats have the reliability and shelf life of magnetic backup tapes! Espeically newer formats like AIT, SAIT, and LTO (and VXA isn't too bad either, awesome pricing on smaller VXA auto loaders). So if you are looking for reliable long term archiving CD and DVD are NOT what you want to use! You want to use tapes. How ever, you can use CD or DVD if you keep in mind that this format has a shorter shelf life and you plan a migration of that data to a new removable media format say 10 years out from now. You have to do the same thing with tapes too, as eventualy formats become old enough that it gets hard to find tape drives that will read your backups. And yes there is still a limit to the shelf life of backup tapes, as over time the magnetic signals encoded in the tape start to transfer between layers due to the tape layers being tightly wound around each other on the take up spool. How ever, even with that in mind, tapes provide a much longer useful life span for archiving data. And beyond having a longer shelf life tapes have several other advantages. They have much larger capacities than CD/DVD media, so you don't have to sit there rotating tons of discs to restore a large archive. And in many cases newer tape formats have much faster transfer rates than CD/DVD (granted they cannot do random I/O, but burning CD/DVD isn't a random I/O process either). Any one who has serious data to protect shouldn't be using CD/DVD for backup. This is more of a cheap low end consumer approach for those who cannot dish out $1000+ for a good tape drive.
Those who still have the wool pulled over theirs eyes and still think CD/DVDs are a long term storage platform need only look to those of us who have very old CDs and laser discs for proof to the contrary. I know plenty of people who bought some of the first pressings of CD albums back in the early 80s, and many of their earlier CDs are now suffering bit rot. This is even more prevelant on laser disc, probably because of the much larger surface area being affected. Many laser disc owners are fully aware of the problem of optical media bit rot. In many cases the bit rot gets bad enough that you can visualy see the distortions on the reflective surface.
Bottom line, if you value your data then use backup tapes! That's what that technology was invented for! CD/DVD-R is more of a short term backup option, best for cheap short term archiving or transporting of data. I use CD/DVD-R for regular backups of the documents on some of my workstations. But when it comes to our servers and our customer's servers it's AIT or LTO tape drives all the way!! Use the right tool for the job!!