Re: Using compression before encryption in device-mapper

["Jörn Engel" <joern@wohnheim.fh-wedel.de>]

On Wed, 14 April 2004 13:44:33 +0100, Paulo Marques wrote:
> Guillaume Lacôte wrote:
> 
> >>>Oops ! I thought it was possible to guarantee with the Huffman encoding
> >>>(which is more basic than Lempev-Zif) that the compressed data use no
> >>>more than 1 bit for every byte (i.e. 12,5% more space).
> 
> WTF??
> 
> Zlib gives a maximum increase of 0.1%  + 12 bytes (from the zlib manual), 
> which for a 512 block will be a 2.4% guaranteed increase.
> 
> I think that zlib already does the "if this is bigger than original, just 
> mark the block type as uncompressed" algorithm internally, so the increase 
> is minimal in the worst case.

Correct, but Guillaume doesn't care about compression efficiency.
"mark the block uncompressed" is precisely what he does *not* want,
unless I got him wrong.

Jörn

-- 
...one more straw can't possibly matter...
-- Kirby Bakken