# understanding negative storage space



## m4rtin (Dec 14, 2011)

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


```
[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%?


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## fluca1978 (Dec 14, 2011)

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.


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## SirDice (Dec 14, 2011)

It's explained a bit in newfs(8):

```
-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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