Re: worse than expected compression ratios with -o compress

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On Mon, 18 Jan 2010, Jim Faulkner wrote:

So, in summary, the compression ratios are:
btrfs: 96%
zip/gzip: 15%
bzip2: 11%
7z: 8%
NTFS: 41%

One minor follow up. I used "mysql < mysqldump.sql" to initially populate the database on the btrfs filesystem. I thought that this may affect the compression ratio, since mysql probably keeps changing the same blocks as the sql import progresses. Compare this to the NTFS test, in which I simply copied the populated database files onto the filesystem.

So, I created a new btrfs filesystem, mounted it with the compress option, and simply copied my database files onto the filesystem, just like I did on the NTFS test. This did make a small difference:
delta-9 mysql # du -h
0       ./btrfs-mysql-test/test
73G     ./btrfs-mysql-test/urd
743K    ./btrfs-mysql-test/mysql
73G     ./btrfs-mysql-test
73G     .

Filesystem            Size  Used Avail Use% Mounted on
/dev/sdi              187G   67G  120G  36% /var/news/mysql

This shaved another 3 GB off of the disk usage, so btrfs has now achieved a 91% compression ratio.

This is still rather poor compared to the 41% compression ratio achieved by NTFS. Surely btrfs should be better at compressing this data.
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