On Sun, May 25, 2003 at 10:00:13AM +0300, Jukka Marin wrote:
> On Sat, May 24, 2003 at 03:41:01PM -0400, Thor Lancelot Simon wrote:
> 
> > They are also significantly more mechanically complex than
> > tapes, and if, for example, put in a safety deposit box that is then
> > exposed to high heat or flooding, are a *lot* less likely to be readable
> > whether with normal or heroic effort.
> 
> I don't think the tapes can take all that much heat, either..

The problem is that "fireproof" containers such as safety deposit
boxes and safes typically resist flame by generating water through an
endothermic reaction with high activation energy.  Tapes will survive
this -- they're designed to -- whereas disks won't.

> > Tapes are not only designed for these purposes, they're tested to ensure
> > that they're suitable for that kind of use -- accellerated and even
> > actual aging tests, heat and water and mechanical wear tests, etc.  Tapes 
> > can be re-spooled, spliced, etc; and I've successfully read 7-track
> > tapes that were several decades old with no trouble at all once I got
> > the 7-track drive working.
> 
> What was the bit density of such tapes?  I trust old disks and tapes more
> than the new ones.  On an IBM XT clone we had a floppy drive which could
> store data on cardboard (well, almost), but the new machines are always
> having problems with floppies.  QIC tapes have never failed in my use,
> but DAT tapes have - and I've had a DAT drive go bad as well.  I haven't
> got a DLT drive yet.

The 7-track tapes were, if I recall correctly, either 400 or 556bpi.  So
yes, a little oxide flaking off here or there would have done a lot less
damage.  On the other hand, one of the design goals of the linear tape
formats like DLT and LTO and the StorageTek stuff is to provide the wear
resistance and reliability over a period of decades that the older
reel-to-reel tape did, and that helical scan formats like Exabyte and
DAT (which have a spinning head with tape moving past it in a different
direction) have been unable to deliver, probably due to their much
greater mechanical complexity and the "consumer" origins of the original
tape formats and transports.

One reason I still have a DEC-branded DLT2500 drive (which is only
15GB and which I could replace with something with more capacity pretty
cheaply) is that it has firmware that will still read the old TK50 tapes
I wrote on my DECstation 10 years ago.  The TK50 SCSI interface was
ghastly and the build quality of the drives wasn't all that good either,
but the tapes still work just fine after 10 years sitting on the shelf
gathering dust...

-- 
 Thor Lancelot Simon	                                      tls@rek.tjls.com
   But as he knew no bad language, he had called him all the names of common
 objects that he could think of, and had screamed: "You lamp!  You towel!  You
 plate!" and so on.              --Sigmund Freud