Following last week's column on backing up data, I received a message from Constance Graves. Constance has been a Mac user for 18 years and she has some valuable information to share concerning backing up important papers using CDs. Constance writes:

I too thought burning CDs was the final answer to storing or archiving stuff from my computer. That is, until I read a lot about the instability of certain CDs. They apparently are not all created equal. I found out by trying to read some of the CDs I had burned previously, discovering that some of the files were unreadable. So much for archiving files. 

There is a bit of controversy about what is the cause of the problem - the media, the burner speed, how we label the CDs, etc. Some people swear by certain brands of CDs. I have found that almost all of the well-known brand name CDs perform satisfactorily - at least for the short run - if you burn at a slow enough speed (no faster than 4X and usually best at 2X) and are VERY careful with how you label the disk. (Oil-based markers are a no-no!)

For really long-term storage I've come to rely on M-O disks. They seem to have a long shelf life and can be written to and erased repeatedly and almost indefinitely without difficulty. The ones I use come in 640MB size although 1.3 gig disks are also available from Fujitsu. The main drawback is that the media are expensive ($25 to 30 per disk). However, it may be a small price to pay for security. The disks are apparently indestructible. 

At this point, having never heard of M-O disks, I wrote Constance and asked her for specific information. Constance wrote:

M-O disks refer to magneto-optical disks. They come in 3-1/2 inch size although they are slightly thicker than regular floppies. The recording medium is plastic which looks very much like a CD only smaller. I don't really understand fully how the drives work except that it's a combination of magnetic and optical, and the disks can be written and rewritten to innumerable times. I use a Fujitsu. FireWire drive which reads and writes to all older, smaller disks (they start at 128 MB) up to the 640 MB The disks themselves are made and sold by a variety of makers - Fujitsu, Sony, etc.

The 640 MB disks are handy in that they have the same capacity as a CD, thus when one is full I can transfer its contents onto a CD. However, as I mentioned yesterday, I still keep the M-O disks for permanent archives as I think they're more trustworthy. The only problem is that because the disks cost so much (one can occasionally get them on sale for as little as $15 each but generally they run around $25-30), it's an expensive way to archive stuff. I think the cost of the media has kept the format from becoming more widely used. Too bad.

I looked up the information I'd read last year about failures of CD-R disks. The URL is: http://www.macintouch.com/cdrfailure.html The information may well curl your hair!

For the nonce I'm archiving things both on CDs and M-O disks (belt and suspenders). For short term storage (temporary back-up for the system file for example) I'm using DVD-RAM. The disks are pretty cheap and can hold a lot of information. Here again I don't know about the long-term stability of the media. That remains to be seen. 

MacInTouch is a great online resource that is considered by many to be the granddaddy of online Mac sites. They post a lot of reader comments about issues, many of them being problems about Macs and Mac products. In the original letter referenced by Constance, the author noted that he had purchased some CDs, saved to them, and verified them. He thought he was all set. He noted that he stored them in a relatively dark, relatively cool room, accessing a few of them about once a month, though several were never touched (after the initial verification test). Then, after an unspecified amount of time he discovered that almost all of the CDs were unreadable. He went on to describe his efforts to read them, noting finally that "So, I have about 5GB worth of coasters that worked originally and gave no warning that they were failing, and I don't have backups (they _were_ my backups!)."

In response to the original letter, information was sent in by someone whose job is in the CD industry. He offered some quick tips for checking out the validity of your CDs.

Hold the disc up towards a light source and check for transparency. If you can see through it like a piece of wax paper, stay clear of this stuff.

If you can see little pin-like holes in the disc, it's a disaster waiting in the wings.

Avoid any hybrid dye products. There are only 3 types of CD-Rs: Azu (blue) dye (Verbatim patent), Cyanine (green) dye (Taiyo Yuden patent), and Phthalocyanine (gold stabilized clear) dye (Mitsui patent). All other CD-Rs, no matter whose name is on it, are either OEMs or hybrids of these three dyes.

And, avoid any media with lots of design "painted" on the surface of the CD-R. This has been proven to interfere with the read and/or write session. CD-Rs with surfaces covered entirely with "paint" are suspect. This technique is usually used to conceal the very, very thin dye layer under the surface.

There is more technical information contained in the letters, but perhaps this gives an idea of what kind of problems can occur. Do I wish I had never brought this up? Not really. Just because I didn't have a clue that this problem exists doesn't mean it isn't something we all probably should know. I am just grateful for readers like Constance who take the time to share information.

If you have any questions, comments, or tips, let me know and I may include them in a future column.