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Syster
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Joined: 26 Jun 2007
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PostPosted: Tue Oct 14, 2008 8:49 am    Post subject: Reiser4 compression won't work? Reply with quote

Hi all! :)
I've tried to test reiser4 acting as additional filesystem. I was wondering how much space i can free using compression.
However, i think compression just won't work;/ So, let's start from the beginning:
I've patched 2.6.25 kernel from portage with reiser4 patch. Also, i've compiled into a kernel reiser4 support (not as module).
Then, i've created a partition using:
Code:
mkfs.reiser4 -o compress=gzip1,compressMode=force /dev/sda6

I've copied 798MB movie file, and checked free space:
Code:
/dev/sda6              28G  693M   28G   3% /mnt/ubuntu

So, unhappy with result, i've aditionally copied 4,3GB of photos.... and df shows me exactly 5GB of used space :(
The last try: copy all portage tree (which weights 217MB), df shows 199MB;/

Why compression is so bad??
Any ideas? Experiences?
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gimpel
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PostPosted: Tue Oct 14, 2008 9:49 am    Post subject: Reply with quote

Movies, given they are in some MPEG format (MPEG, AVI container), are already compressed.
Same counts for OGG, MP3, JPEG and other compressed media files.

All that can be compressed is the header data, that's why it results in a just a little bit smaller file.

Try to gzip some Movie file. The result will be the same.
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hirakendu
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PostPosted: Tue Oct 14, 2008 10:47 am    Post subject: Reply with quote

true, you can't compress files already compressed (especially lempel-ziv'ed ;)). only text files and possibly (sparse) binaries and such.
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dusanc
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PostPosted: Tue Oct 14, 2008 4:19 pm    Post subject: Reply with quote

And R4+cc is smart enough that it evaluates if file is compressible (but not for you as you checked force ) so that no CPU time is wasted on compressing uncompressable files.
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mbar
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PostPosted: Wed Oct 15, 2008 7:17 am    Post subject: Reply with quote

I think you forgot to use "create=ccreg40" option also.
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kernelOfTruth
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Joined: 20 Dec 2005
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Location: Vienna, Austria; Germany; hello world :)

PostPosted: Thu Oct 16, 2008 6:38 pm    Post subject: Reply with quote

mbar wrote:
I think you forgot to use "create=ccreg40" option also.


indeed!

@Syster:

have a look at https://forums.gentoo.org/viewtopic-t-707465.html for an in-depth view on reiser4 formatting options :wink:

you could, of course, set reiser4 to force compression upon every file but it could take ages to copy a single file ...
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