Re: compression disk space saving - what are your results?

[Marc Joliet <marcec@gmx.de>]

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On Wednesday 02 December 2015 18:46:30 Tomasz Chmielewski wrote:
>What are your disk space savings when using btrfs with compression?
>
>I have a 200 GB btrfs filesystem which uses compress=zlib, only stores
>text files (logs), mostly multi-gigabyte files.
>
>
>It's a "single" filesystem, so "df" output matches "btrfs fi df":
>
># df -h
>Filesystem      Size  Used Avail Use% Mounted on
>(...)
>/dev/xvdb       200G  124G   76G  62% /var/log/remote
>
>
># du -sh /var/log/remote/
>153G    /var/log/remote/
>
>
> From these numbers (124 GB used where data size is 153 GB), it appears
>that we save around 20% with zlib compression enabled.
>Is 20% reasonable saving for zlib? Typically text compresses much better
>with that algorithm, although I understand that we have several
>limitations when applying that on a filesystem level.
>
>
>Tomasz Chmielewski
>http://wpkg.org

I have a total of three file systems that use compression, on a desktop and a 
laptop.  / on both uses compress=lzo, and my backup drive uses compress=zlib 
(my RAID1 FS does not use compression).  My desktop looks like this:

% df -h
Dateisystem    Größe Benutzt Verf. Verw% Eingehängt auf
/dev/sda1       108G     79G   26G   76% /
[...]

For / I get a total of about 8G or at least 9% space saving:

# du -hsc /mnt/rootfs/*
71G     /mnt/rootfs/home
14G     /mnt/rootfs/rootfs
2,3G    /mnt/rootfs/var
87G     insgesamt

I write "at least" because this does not include snapshots.  On my laptop the 
difference is merely 1 GB (83 vs. 84 GB), but it was using the autodefrag 
mount option until yesterday (when I migrated it to an SSD using dd), which 
probably accounts for a significant amount of wasted space.  I'll see how it 
develops over the next two weeks, but I expect the ratio to become similar to 
my desktop (probably less, since there is also a lot of music on there).

I would love to answer the question for my backup drive, but du took too long 
(> 1 h) so I stopped it :-( .  I might try it again later, but no promises!

Greetings
-- 
Marc Joliet
--
"People who think they know everything really annoy those of us who know we
don't" - Bjarne Stroustrup

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