This is version 0.4l of what was an fs-independent disk compression driver
for Linux: DouBle (see below for an explanation of "was").

It is compatible with previous versions, but once used with version 0.3
or 0.4, compressed devices will not be compatible with older versions,
_even_ if they had been created with previous versions.
Most utilities from 0.2 or 0.3 need to be upgraded to 0.4, and codes for
compression algorithms have changed in 0.3.

The primary focus of version 0.4 has been on improving the behavior of
DouBle when devices run out of space. This is achieved through a good bit
of cooperation between DouBle and ext2. Corollaries:
- it works better only if you use DouBle for an ext2 fs.
- it's not totally fs-independent anymore (but it'll work as before for
other fs and other purposes).
- it is not 100% secure (I guess it'll never be). Just more than before.

The other major news is that it now works on MSDOS filesystems - DouBle
devices can now be regular MSDOS or UMSDOS files and one can build an
MSDOS filesystem on a DouBle device as well.

A new block allocation scheme, designed to prevent fragmentation, has
been implemented - and there's a new utility to check fragmentation.

Very importantly also, speed has been improved significantly in
version 0.4d.

dbck can now repair quite a few problems (because bugs in versions 0.4a
and 0.4b had corrupted all my compressed devices). There's a clean bit,
which should get cleared when devices are not dismounted cleanly and reset
when dbck exits with no errors.

With respect to double 0.4i, this version fixes one bug that could yield
device corruption while (u)mounting other devices and it comes with a patch
against Linux kernel 1.2.5.

WARNING: Although Double-0.4l would patch Linux > 1.1.95 to 1.2.3 easily,
DO NOT USE Double 0.4k with kernels older than 1.2.4.

There have been a good number of bug fixes in recent versions, but it is
possible that some remain and that new ones have been introduced (you've
been warned).

Please note that as of Linux 1.1.95, major #19 is also used for the cyclades
mux driver (char driver) - I don't know what kind of problem this may be to
people using this new driver.

Before installing, read the HOWTO file carefully.

In case of problem, do not hesitate to get in touch with me

Jean-Marc Verbavatz <jmv@achaz.saclay.cea.fr> 
