Rob Studdert wrote:
On 2 Dec 2005 at 0:32, Toralf Lund wrote:
Tapes are the most commonly used media for backups on large computer
systems. They have a longer expected shelf lifetime than anything else.
In other words a back-up solution not quite equivalent to the cost of DVD
burner and 100 quality DVD media. The shelf lifetime for tapes (or any other
magnetic media) is likely more limited than read only optical media. The
magnetized tape loses it's magnetization over time and oxide binders fail, I've
had a lot to do with digital and analogue tape media in the past.
I haven't been around for that long, so I obviously can't verify the
claim, but I believe that some of the manufacturers of high-quality
tapes say that they have a lifetime of at least 50 years. And it's based
on someone's experience, I guess - tape technology has been around for
rather a long time (so it is at least more well-tested than the optical
one.) Also, I think the loss of magnetisation you talk about is in a
sense gradual loss of data - rather like with film actually (although an
actual bit of data will either be read correctly or not, obviously) -
where optical media is perhaps expected to fail more instantaneously
(like I said.)
I haven't seen it myself, either. But some of the people who use CDs for
professional archival will renew them (as in copying the data to new
medium) every 5 years. Apparently, they are most concerned about media
separation, i.e. that the disc literally falls apart.
DVD media is a constructed as sealed polycarbonate sandwich, they should not
suffer the potential effects
Well, DVDs certainly look more robust...
on the data layer that may effect CDs if a
poor/faulty lacquer was used.
The situation was probably a lot worse than it is today a few
years ago, though, when CD writers were young and inexperienced, to put
it that way...
I've still got discs written on the earliest Philips CD-R burners and they are
absolutely fine.
I've also got some rather old CDs in a shelf in my office, and I *think*
I can read them. However, I probably also threw away two CDs before I
got each of them because the burn operation never would work on the
first attempt, and probably not the 2nd, either. Or maybe I'm
exaggerating now, but I'm quite sure that the failure rate was a lot
higher when I started writing CDs than it is today...
- T
