disk fragmentation

Dan Nelson dnelson at allantgroup.com
Tue Feb 1 12:46:52 PST 2005

In the last episode (Feb 01), Jim Pazarena said:
> during the boot sequence, I routinely see a "% fragmentation
> message".
> It was my understanding that fragmentation doesn't occur on a Unix
> (er FreeBSD) box..
> It seems that there is a concept of fragmentation from the above
> message, so, is there an "un-fragment" utility?

In the ffs filesystem, a file that's smaller than the default 16k
blocksize (or the last part of a file that doesn't completely fit into
a block) doesn't have to waste an entire block.  Blocks can be split
into eight 2k fragments and small files are put in them.  The "%
fragmentation" is just the percentage of fragment blocks vs the total
number blocks.  It's more an indicator of how many small files you have
in the system than anything else.

	Dan Nelson
	dnelson at allantgroup.com

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