disk fragmentation, <0%?

[Lei Sun]

Hi,

I know this question has been raised a lot of times, and most of
people don't think it is necessary to defragment ufs, and from the
previous posts, I got to know there are sometimes, disksize can be
more than 100%

But...

I got ...

/dev/ar0s1a: ... 0.5% fragmentation
/dev/ar0s1e: ... 0.0% fragmentation
/dev/ar0s1f: ... 0.0% fragmentation
/dev/ar0s1d: ... 0.1% fragmentation

Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/ar0s1a    248M     53M    175M    23%    /
devfs          1.0K    1.0K      0B   100%    /dev
/dev/ar0s1e    248M   -278K    228M    -0%    /tmp
/dev/ar0s1f    221G    1.4G    202G     1%    /usr
/dev/ar0s1d    248M     30M    197M    13%    /var

My questions:
1. How do I make /dev/ar0s1a 0.0% fragmentation the clean way? If I
really wanted to?

2. How come /tmp is -0% in size? -278K? What had happened? as I have
never experienced this in the previous installs on the exact same
hardware.

Thanks 

Lei