linux-kernel - Re: Reiser4. BEST FILESYSTEM EVER.

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Date:	Sat, 07 Apr 2007 13:21:05 -0400
From:	Valdis.Kletnieks@...edu
To:	Krzysztof Halasa <khc@...waw.pl>
Cc:	johnrobertbanks@...tmail.fm, Jan Harkes <jaharkes@...cmu.edu>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Reiser4. BEST FILESYSTEM EVER.

On Sat, 07 Apr 2007 16:11:46 +0200, Krzysztof Halasa said:
>
> Gzip - 3 files (zeros only, raw DV data from video camera, x86_64
> kernel rpm file), 10 MB of data (10*1024*1024),
> $ l -Ggh zeros dv bin
> -rw-r--r-- 1 10M Apr  7 15:30 bin
> -rw-r--r-- 1 10M Apr  7 15:31 dv
> -rw-r--r-- 1 10M Apr  7 15:31 zeros

> $ l -Ggh zeros.gz dv.gz bin.gz
> -rw-r--r-- 1  10K Apr  7 15:31 zeros.gz
> -rw-r--r-- 1 9.1M Apr  7 15:31 dv.gz
> -rw-r--r-- 1 9.3M Apr  7 15:30 bin.gz
> 
> ... and though the numbers may still sound impressive, space savings
> are less than 10%.

I am quite sure that the kernel RPM file is *already* compressed, at least
somewhat.  Otherwise, it's hard to explain this:

-rw-r--r--    1 529      263     17835757   Apr  5 00:19   kernel-2.6.20-1.3045.fc7.x86_64.rpm

% du -s /lib/modules/2.6.20-1.3038.fc7/
76436   /lib/modules/2.6.20-1.3038.fc7/

and it can't all be slack space at ends of files:

% find /lib/modules/2.6.20-1.3038.fc7/ -type f | wc -l
1482

Even on a 4K filesystem, the *max* wasted slack would be about 4M.

And what do you know - if you tar.gz that /lib/modules:

% tar czf /tmp/kern.tar.gz /lib/modules/2.6.20-1.3038.fc7/
tar: Removing leading `/' from member names
% ls -l /tmp/kern.tar.gz 
-rw-r--r-- 1 valdis valdis 15506359 2007-04-07 13:19 /tmp/kern.tar.gz

The *compressed* tar is about 15M (remember the .rpm contained a 2M vmlinuz
as well - that;s compressed too).  So we're right up to the 17M of the .rpm,
which indicates that the RPM is compressed at a factor close to tar.gz.

I'd not be surprised to find out that your digital-video also contains
at least some light compression - if it's mpeg or similar, that's already
had some *heavy* compression done to it....

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