On 10/18/07, Iverson, Jerald <Jerald.Iverson AT aiminvestments DOT com> wrote:
> ...
> that is why i have turned off all hardware and software compression on
> my tape drives.  imagine trying to store more than 400GB of data onto a
> single lto3 tape!  they "say" that you can store up to and even more
> than 800GB, but i don't believe a word of it.  there is no way 1 nibble
> of data can represent 1 byte!  once i have the time to study lzr
> compression and understand it,
<snip>

Hi jerald,

Data compression exploits the non-randomness of "normal" data.
Compression algorithms have variable compression rates because their
performance is dependent on the data being compressed.    Truly random
data does NOT compress at all.   "Typical" data is not truly random.
Once data has been compressed, it is close to random, so compression
can not be applied again.  Many encryption algorithms also result in
near-random data that does not compress.

A formal definition of a data set's "randomness" is it's Kolmogorov
complexity. http://en.wikipedia.org/wiki/Kolmogorov_complexity

Compression is just an alternate means of data representation.
Several others are at work on your LTO tapes too!
http://en.wikipedia.org/wiki/Forward_error_correction
http://en.wikipedia.org/wiki/Run_Length_Limited
http://en.wikipedia.org/wiki/PRML

Don't get too paranoid...these are good things.

Austin
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