understanding negative storage space

M

m4rtin

According to df(1), I have -5.3MB free space on my /dev/ad6s1a partition:

Code: 
[root@ ~]# df -h
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/ad6s1a    496M    461M   -5.3M   101%    /
devfs          1.0K    1.0K      0B   100%    /dev
/dev/ad6s1e    496M    6.3M    450M     1%    /tmp
/dev/ad6s1f     70G     14G     50G    22%    /usr
/dev/ad6s1d    1.9G    110M    1.7G     6%    /var
[root@ ~]#

How to understand this? :OO And why aren't maximum amount of data stored on the partition 100%?
 
UFS/FFS reserve a certain amount of space for several reasons: mainly performance and avoiding disk fill (as root you will be glad about this). You are simply seeing that your user level (allow me to call it) space has overlapped this reserved space, so you should try to free space to give FFS a chance to work better. See this and the mount command man page.
 
It's explained a bit in newfs(8):
Code: 
     -m free-space
             The percentage of space reserved from normal users; the minimum
             free space threshold.  The default value used is defined by
             MINFREE from <ufs/ffs/fs.h>, currently 8%.  See tunefs(8) for
             more details on how to set this option.

It's best not to fiddle with it.
 
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