From owner-freebsd-questions  Thu Sep 24 03:51:31 1998
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Date: Thu, 24 Sep 1998 12:50:50 +0200 (CEST)
From: Konrad Heuer <kheuer@gwdu60.gwdg.de>
To: Peter Kok <peter@sweda.com.hk>
cc: freebsd <freebsd-questions@FreeBSD.ORG>
Subject: Re: fragmentation
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On Thu, 24 Sep 1998, Peter Kok wrote:

> After boot up a computer, there is message prompted
> 
> /dev/rmd0s2a: clean, 17705 free (313 frags, 2174 blocks, 1.0
> fragmentation)
> 
> what is the meaning of frags?  and how do you do defragmentation? 

You don't need to defragment a FreeBSD file system (which is essentially a
4.2BSD fast file system (ffs)).

The file system typically uses 8K blocks of disk space. Since files are
often smaller a file can use fragments (typically 1K) of a block. To be
more precise, the last block of a file may be fragmented.

Fragmentation you probably think of is spreading all the blocks of a file
over the disk. The Berkeley ffs implements very intelligent algorithms to
prevent this and to optimize file system throughput. 

Take a look at the system documentation:
gunzip < /usr/share/doc/smm/05.fastfs/paper.ascii.gz | more

Regards
Konrad Heuer

// Gesellschaft fuer wissenschaftliche Datenverarbeitung mbH
// Goettingen (GWDG), Am Fassberg, D-37077 Goettingen, Germany
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// kheuer@gwdu60.gwdg.de


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