Re: Transparent compression in the FS

[P]

Andrea Arcangeli wrote:
> Hi Jeff,
>
> On Wed, Oct 15, 2003 at 11:13:27AM -0400, Jeff Garzik wrote:
>
> > Josh and others should take a look at Plan9's venti file storage method 
> > -- archival storage is a series of unordered blocks, all of which are 
> > indexed by the sha1 hash of their contents.  This magically coalesces 
> > all duplicate blocks by its very nature, including the loooooong runs of 
> > zeroes that you'll find in many filesystems.  I bet savings on "all 
> > bytes in this block are zero" are worth a bunch right there.
>
> I had a few ideas on the above.
>
> if the zero blocks are the problem, there's a tool called zum that nukes
> them and replaces them with holes. I use it sometime, example:

Yes post processing with this tool is useful.
Also note gnu cp (--sparse) inserts holes
in files also.

I thought a bit about this also and thought
that in general the overhead of instant block/file
duplicate merging is not worth it. Periodic
post processing with a merging tool is
much more efficient IMHO. Of course this is
now only possible at the file level, but this
is all that generally useful I think. I guess
it's appropriate to plug my merging tool here :-)
http://www.pixelbeat.org/fslint

Pádraig.

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