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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.unix.wizards
Subject: Re: Disk Fragmentation
Message-ID: <24326@sun.uucp>
Date: Tue, 28-Jul-87 14:15:25 EDT
Article-I.D.: sun.24326
Posted: Tue Jul 28 14:15:25 1987
Date-Received: Thu, 30-Jul-87 02:18:08 EDT
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> SystemV has just such a utility:  dcopy(1M).  It's man page claims it will
> deflate large empty directories and place file blocks with optimal
> rotational gap.  Also subdirectories are placed at the beginning of a
> directory in hopes of speeding depth first directory searches.  Given that
> AT&T went to the trouble to do this, cp(1) sounds too easy (and no directory
> re-organization is done to the best of my knowledge.)  

The secret here is that, indeed, the original posting *was* about
4.3BSD.  The 4.[23]BSD file system uses a bitmap, not a free list, to
keep track of free blocks, and when a new block is needed it tries as
best it can to allocate one radially as close to a related block as
possible, preferably (at least in the case of blocks in a file)
rotationally positioned as optimally as possible as well.  It also
tries to keep directories close to the files in them; the 4.3BSD
version will also deflate large directories when possible.
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com