Hi Folks,
I often to use CDs to back up archival files.
No problems so far. However, I've heard tell that CDs can degrade over time and that times of the order of 4 years might be the point where they start to get dodgy.
Is this the case? If so, does it vary with the brand/type of CD? And does something similar apply to DVDs?
Thanks, Ted.
-------------------------------------------------------------------- E-Mail: (Ted Harding) Ted.Harding@nessie.mcc.ac.uk Fax-to-email: +44 (0)870 094 0861 Date: 09-Jun-06 Time: 19:30:10 ------------------------------ XFMail ------------------------------
On Fri, Jun 09, 2006 at 07:30:12PM +0100, Ted Harding wrote:
Is this the case? If so, does it vary with the brand/type of CD? And does something similar apply to DVDs?
My opinion is don't worry about it. My evidential data on this is recently (in the past 3 months) I destroyed some old backups that were taken in 2000 (the data was either moved to newer backups and put on different storage first, obviously) and they all worked *perfectly* despite many of them being abused. The other test data was that of some mp3 CD's I burned for listening to on the in car mp3 player. I purchased the in car player 3 years ago and recently stuck it in my new car, I also grabbed some of the CD's that had been in the old car for 3 years, all of them were ok apart from one that had a *big* scratch in it. Given that these discs have survived living in a car (on the floor, in the door pockets etc.) mostly without cases and the extremes of heat/cold that they were subjected to in there and that they had dozens of scratches on them told me not to worry about archival backups, which certainly don't have such a hard life. I think the main problem with the dyes used in CD-R discs is that they are not "light fast" so you may want to make sure they are in a dark place (inside the fire safe suits me fine), it also does apply to DVD's but I think that the more modern compositions of dyes used in the discs are better than the original dyes used for the very early burners/discs.
Current strategy for me is to put backups into the fire safe designed for computer media (this will help wrt to big fires and environmental concerns like humidity and light) burn 2 sets of discs onto different brands of media "just in case" and make sure I take a full backup every so often and keep the older copies to hand. I also test the old backups when they need to be replaced to make space in the safe and so far all of them have been fine. I also only write on the sleeves (I use sleeves to minimise the risk that the discs get scratched) that the discs go into just in case the ink in the pens I use decided to have a chemical composition that eats plastic. I'm certain that this strategy is a bit OTT for what I need, but in the case of backups I'd rather overspecify a bit than to try to be a cheapskate.
Thanks Adam
On Fri, Jun 09, 2006 at 07:56:09PM +0100, Adam Bower wrote:
On Fri, Jun 09, 2006 at 07:30:12PM +0100, Ted Harding wrote:
Is this the case? If so, does it vary with the brand/type of CD? And does something similar apply to DVDs?
My opinion is don't worry about it. My evidential data on this is recently (in the past 3 months) I destroyed some old backups that were taken in 2000 (the data was either moved to newer backups and put on different storage first, obviously) and they all worked *perfectly* despite many of them being abused. The other test data was that of some mp3 CD's I burned for listening to on the in car mp3 player. I purchased the in car player 3 years ago and recently stuck it in my new car, I also grabbed some of the CD's that had been in the old car for 3 years, all of them were ok apart from one that had a *big* scratch in it. Given that these discs have survived living in a car (on the floor, in the door pockets etc.) mostly without cases and the extremes of heat/cold that they were subjected to in there and that they had dozens of scratches on them told me not to worry about archival backups, which certainly don't have such a hard life. I think the main problem with the dyes used in CD-R discs is that they are not "light fast" so you may want to make sure they are in a dark place (inside the fire safe suits me fine), it also does apply to DVD's but I think that the more modern compositions of dyes used in the discs are better than the original dyes used for the very early burners/discs.
A couple of years ago I read an article discussing that there are a few different chemical systems underlying writable CDs, and that these have huge differences in half-life and sensitivity to various kinds of abuse (i.e. some may be sensitive to light, others to heat, or to humidity etc.).
There also appear to be differences in manufacturing quality, in some cheap media, the chemical layers are not properly sealed in the transparent plastic, exposing the chemical layers to aerial oxygen which then slowly degrades them over time.
Unfortunately, I don't remember the details and all I can find with a quick google search is
http://www.rense.com/general52/themythofthe100year.htm
It seems to me that in order to reliably assess the durability of CDs, information on the underlying technical layers is required.
Best regards, Jan
On Friday 09 June 2006 19:56, Adam Bower wrote:
On Fri, Jun 09, 2006 at 07:30:12PM +0100, Ted Harding wrote:
Is this the case? If so, does it vary with the brand/type of CD? And does something similar apply to DVDs?
I'd just like to chime in and say that I've had experiences with CD-Rs in the past just "becoming blank" with time - including on one occasion several redundant versions of the same archive.
I've kept them away from light, impact, changed the way I've burned them, and everything else, but I just couldn't escape the unreliability of 3billion-per-penny CDs, so I started to fork out for decent media and stopped having problems (bar the occasional coaster burnt :-) )
I've found that if you buy very cheap media, you stand a much higher chance of losing the data. Not one to discourage thrift usually, but certainly where CDs are concerned, my advice would be yes, buy the expensive branded ones - and certainly never use cheap CD media as the sole storage for any data you care about.
I've kept to the same idea with DVDs, but I hardly burn to DVDs at all, so I've never encountered problems and never used cheap burnable DVDs.
HTH
-
Adam Bower -
Jan T. Kim -
Ted.Harding＠nessie.mcc.ac.uk -
Ten