Minus on disk:-)

[Brian A. Seklecki]

On Wed, 2007-03-21 at 21:11 +0100, Anders Troback wrote:
> Disk status:
> Filesystem  1K-blocks      Used    Avail Capacity  Mounted on
> /dev/ad8s2a    253678    124556   108828    53%    /
> devfs               1         1        0   100%    /dev
> /dev/ad8s2g  35796214  16027612 16904906    49%    /home
> /dev/ad8s2e   1012974        -6   931944    -0%    /tmp
> /dev/ad8s2f  20308398  15124786  3558942    81%    /usr
> /dev/ad8s2d   1012974    258006   673932    28%    /var
> 
> Hi,
> 
> I'm just curious about this! How can a FS have used -6 bytes?

By default, 8% of capacity is reserved for UID0 (root) and is not
represented in df(1).  Read tunefs(8):

     -m minfree
             Specify the percentage of space held back from normal users; the
             minimum free space threshold.  The default value used is 8%.
             Note that lowering the threshold can adversely affect perfor-
             mance:

             o   Settings of 5% and less force space optimization to always be
                 used which will greatly increase the overhead for file
                 writes.

             o   The file system's ability to avoid fragmentation will be
                 reduced when the total free space, including the reserve,
                 drops below 15%.  As free space approaches zero, throughput
                 can degrade by up to a factor of three over the performance
                 obtained at a 10% threshold.

             If the value is raised above the current usage level, users will
             be unable to allocate files until enough files have been deleted
             to get under the higher threshold.

Try this in fstab(5):

md          /tmp        mfs rw,-s64m,-m0    2   0

~BAS

> 
> As I said this is not a problem, I'm just curios about how things work
> (and can someone please tell me how to make that a -100 Gb:-))
> 
> Thanks!