> On Sun, Apr 23, 2006 at 01:31:44AM +0200, Hubert Feyrer wrote:
> > "Input" data is fixed size (== pagesize), but "output" size depends on the
> > compression factor, and thus you'll need some way to arrange things with a
> > non-fixed offset. Worse, if you replace a page with something that
> > compresses worse, you may not be able to use available space.
>
> Anyone which wants to work on this should really take a look at the
> design of Stacker or Doublespace/Drivespace. The German "PC Intern" in
> version 5 or so descriped the latter. Good reading for an introduction
> to this problem.

Note that OpenSolaris ZFS already contains compression, and they
have just set up a project to add pluggable encryption to ZFS.
It might be worth while checking out the ZFS sources to see how
they solved the variable compressed block size problem:

http://cvs.opensolaris.org/source/xref/on/usr/src/uts/common/fs/zfs/


Regards -- Volker
-- 
------------------------------------------------------------------------
Volker A. Brandt                  Consulting and Support for Sun Solaris
Brandt & Brandt Computer GmbH              WWW: http://www.bb-c.de/~vab/
Meckenheim, Germany                                   Email: vab@bb-c.de