disk fragmentation, <0%?

[Glenn Dawson]

At 11:54 PM 8/13/2005, Lei Sun wrote:
>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?

You don't.  The term "fragmentation" does not mean the same thing in 
FreeBSD that it does in other OS's. (ie windows)

Fragmentation in FreeBSD refers to blocks that have not been fully 
allocated.  For example, if I have a file system that has 16K blocks, and 
2K fragments (think of fragments as sub-blocks if it helps), and I save an 
18K file, it will occupy 1 block and 1 fragment from the next block.  That 
second block then is said to be "fragmented".

In the windows world, fragmentation refers to files which occupy 
non-contiguous groups of blocks.  For example, you might have 5 blocks in a 
row, and then have to move to another part of the disk to read the next 5 
blocks.


>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.

Not sure about that one.  Maybe someone else has an answer.

-Glenn


>Thanks
>
>Lei
>_______________________________________________
>freebsd-questions at freebsd.org mailing list
>http://lists.freebsd.org/mailman/listinfo/freebsd-questions
>To unsubscribe, send any mail to "freebsd-questions-unsubscribe at freebsd.org"