Re: Wrong free space reported for XFS filesystem

[Richard Mittendorfer]

Also sprach "Jesper Juhl" <jesper.juhl@xxxxxxxxx> (Wed, 6 Sep 2006
10:54:34 +0200):
> For your information;
> 
> I've been running a bunch of benchmarks on a 250GB XFS filesystem.
> After the benchmarks had run for a few hours and almost filled up the
> fs, I removed all the files and did a "df -h" with interresting
> results :
> 
> /dev/mapper/Data1-test
>                      250G  -64Z  251G 101% /mnt/test
> 
[...] 
> I then did an umount and remount of the filesystem and then things
> look more sane :
> 
> "df -h" :
> /dev/mapper/Data1-test
>                       250G  126M  250G   1% /mnt/test
[...]
> The filesystem is mounted like this :
> 
> /dev/mapper/Data1-test on /mnt/test type xfs
> (rw,noatime,ihashsize=64433,logdev=/dev/Log1/test_log,usrquota)

I once (2.6.12?) had to copy a quite large directory to an XFS
partition. It "should" had fit onto it (by what df said), but I ran into
"disk full". I think the reason was related to a large xfsbufd_centisecs
or xfssyncd_centisecs and indeed I could watch free space to grow and
shrink in regulaer intervals (watch df -k). I may well be wrong here (as
I'm sure no XFS-expert), but it looked like old data gets some kind of
"comressed" or "ordered" by the XFS-driver while newly written data took
more place. A "slow" copy did it, as well as a later try to an reiserfs
or ext.

sl ritch
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