how good is the data reliability with CD ROM and DVD RAM?

Grant Taylor cctalk at
Tue Jul 24 12:55:15 CDT 2018

On 7/23/18 9:51 AM, Alexander Schreiber via cctalk wrote:
> Another thing to keep in mind: it is nice if your backup medium lasts 
> decades, but what about the reader for it? Will that be available 
> down the road as well and usable?

I seem to recall reading about a ""tape drive that wrote optically to 
the medium in such a way that it could be read optically without overly 
complex magnification.  I want to say something between a good 
magnifying glass and a cheap microscope allowed people with nominally 
20/20 vision to be able to read the bits on the tape.

The tape also purportedly had a leader that was direction on how to read 
the tape manually (optically).

The idea was that it was possible (all be it tedious) for a human to 
read the tape and gain access to the contents there in.

> And, not to forget: what format are your backups written in. Something 
> standard like POSIX tar or some proprietary format used by some 
> commercial software, which might have availability issues in the 
> future.


I've read a few discussions where some of the oldest and biggest formats 
that take up the most space are the most likely to be recovered.  ASCII 
text being one of the most likely.

If you do use a less open / more proprietary format make sure to be 
mindful of what sort of blocking / chunking that it does.  The idea 
being that you don't want corruption somewhere in the tape to render the 
rest of the tape inaccessible.

This also nods towards redundancy.  Having multiple copies of the same 
data different places on the tape and / or on multiple tapes makes it 
much more likely that if (read: when) corruption occurs, you don't 
actually have data loss because ideally redundant copies are good.  Or 
at least between all of the copies you have at least one good aggregate 
copy of the data.

Grant. . . .
unix || die

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