Is it really worth buying CDs?

[rkyburz]

I know almost nothing about optical media, computers etc (when I was at university the computer was the size of a garden shed - an Elliot 803 if memory serves). Over more than 25 years I have never had a commercial cd fail. Presumably these are superior (and the blanks much more expensive) to those one burns oneself?

I have worked on such garden sheds myself — that was a fun time!

CD-R vs. commercial CD: That's an entirely different story: commercial CDs are pressed, not "burned", i.e., the bits are engraved into the layer of aluminum — the worst that can normally happen there is that you scratch it (and even such scratches can often be repaired); I have seen occasional bad CDs — but those were bad right from production (like: one CD had an incomplete aluminum layer) — if kept well, they will take *much* longer to go bad. With CD-Rs you are not burning holes into the aluminum layer, but a laser beam is heating a tiny volume in the data layer, causing it to change its optical properties (and in the case of CD-RW or DVD-RAM that process is even reversible) — that process itself is much more fragile, and so is the stored information.

Correction: with CDs (as with CD-R etc.) the engraving is in the (transparent) polycarbonate layer, not in the reflective aluminum — but it is still pressed, not "burned", so I believe the rest of my statement above is still largely correct (ignoring the bronzing issue).

[Bryn]

I have worked on such garden sheds myself — that was a fun time!

CD-R vs. commercial CD: That's an entirely different story: commercial CDs are pressed, not "burned", i.e., the bits are engraved into the layer of aluminum — the worst that can normally happen there is that you scratch it (and even such scratches can often be repaired); I have seen occasional bad CDs — but those were bad right from production (like: one CD had an incomplete aluminum layer) — if kept well, they will take *much* longer to go bad. With CD-Rs you are not burning holes into the aluminum layer, but a laser beam is heating a tiny volume in the data layer, causing it to change its optical properties (and in the case of CD-RW or DVD-RAM that process is even reversible) — that process itself is much more fragile, and so is the stored information.

I have had more than a dozen PDO pressed CDs fail due to 'bronzing'.

[hafod]

I have worked on such garden sheds myself — that was a fun time!

CD-R vs. commercial CD: That's an entirely different story: commercial CDs are pressed, not "burned", i.e., the bits are engraved into the layer of aluminum — the worst that can normally happen there is that you scratch it (and even such scratches can often be repaired); I have seen occasional bad CDs — but those were bad right from production (like: one CD had an incomplete aluminum layer) — if kept well, they will take *much* longer to go bad. With CD-Rs you are not burning holes into the aluminum layer, but a laser beam is heating a tiny volume in the data layer, causing it to change its optical properties (and in the case of CD-RW or DVD-RAM that process is even reversible) — that process itself is much more fragile, and so is the stored information.

Thank you for that informative response - the more so for me because of a most welcome absence of jargon.

[rkyburz]

I have had more than a dozen PDO pressed CDs fail due to 'bronzing'.

Ah, lucky me — I wasn't really collecting CDs in large numbers yet at the time when (the bulk of) those were manufactured ... :) I guess (hope!) that today's CDs are not (that) susceptible to bronzing, and I can't remember seeing even a single one in my collection (of now about 2000 CDs) turn brownish ... keeping my fingers crossed ...

[Stunsworth]

I guess (hope!) that today's CDs are not (that) susceptible to bronzing, and I can't remember seeing even a single one in my collection (of now about 2000 CDs) turn brownish ... keeping my fingers crossed ...

From memory it was a problem at the Philips plant near Blackburn. If a CD hasn't bronzed by now then it's unlikely to do so in the future. The only problem I've had was with a couple of Hyperion CDs, and the company replaced them for me at no cost.

[scottycelt]

Even if you just use single-sided optical, writable media, and even if you are careful not to use felt pens, sticky labels, etc. to label the discs: writable optical media have a *very* finite lifetime — I would not count on such media to last more than a couple years; if this is your backup, then you want to make 2, better 3 copies — and with this, the effective capacity of a single-sided DVD (4.7 GB) is about that of 2 CDs (800 MB each) ... ;-)

Interesting, but I have plenty of still workable DVD backups that have lasted for much longer than two years. As others have pointed out even external hard disks can fail and if you have EVERYTHING on that, well, suddenly multiple DVDs might have seemed to have been by far the better choice!

The simple truth is there is no completely safe option though your recommendation of more than one backup is obviously the safest of all options.

[johnb]

If you use CD-Rs or DVDs for backup it is best to keep them in a cool, dry, dark place, e.g. in a box. Being left in the light, especially where direct sunlight falls, will greatly lessen their life. (I have CD-Rs that are 5 to 7 years old that play fine.)

Bryn mentioned that he only uses branded discs. Well that can be problematic as some brands are better than others (Memorex used to have a very bad reputation). I rarely use CD-Rs or DVDs these days but for many years I have used Taiyo Yuden discs (which come unbranded) as they have a very good reputation and have never let me down and I have never had a 'coaster'. They are available online in packs of 50.

As far as external hard drives failing - the main issue with external hard drives is overheating due to poor heat dissipation. For that reason it is very important to have them vertical, NOT flat. Ever since a WD MyBook drive failed on me (the HDD was OK but the electronics had fried) I have bought enclosures and fitted my choice of HDD into them - always using "green" low power HDDs, usually either WD or Samsung.

Having said all that, yes HDDs do eventually fail but that is the whole point of having a copy - it is very unlikely that both will fail at the same time. Also, if an external HDD is only used for backup purposes its use will be slight and should have a life much, much longer than a HDD which is in regular use in a PC.

I can also recommend using a utility to monitor HDD temperatures and their health (especially useful for external HDD temperatures). I've used "HD Sentinel" for some years, though there are other programmes which do the same job.