[Gllug] Loopback mountable image file compression.

[Martin Dengler]

On Tue, Sep 01, 2009 at 04:56:07PM +0100, Richard Jones wrote:
> On Tue, Sep 01, 2009 at 03:43:29PM +0100, James Courtier-Dutton wrote:
> > 2009/8/26 Phillip Lougher <phillip.lougher at gmail.com>:
> > >
> > > 3. Sparse block handling.  Squashfs detects holes (zero filled ranges)
> > > and handles them specially.  Cloop compresses zero filled blocks,
> > > leading to worse performance and compression.  Filesystem images often
> > > have very large ranges of zero filled blocks (unused blocks).
> > 
> > Is there a tool to go through an ext3 partition and fill the unused
> > space with zero fill?
> 
> zerofree
> 
> > Can this be done after the ext3 image has been squashfs, thus
> > resulting in a smaller squashfs image?
> 
> No, but you could run zerofree on the ext3 image and then compress
> it.

It may be even better to do something using resize2fs -M or -P.
Better to not use the space than to fill it with zeroes and compress
it (consider streaming uncompression...).

> Rich.

Martin
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