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From: alan@shodha.dec.com ( Alan's Home for Wayward Notes File.)
Newsgroups: comp.unix.ultrix
Subject: Re: Any disk de-fragmenters out there?
Summary: Is there really?
Message-ID: <501@shodha.dec.com>
Date: 30 Nov 89 02:24:59 GMT
References: <2095@compugen.>
Distribution: comp
Organization: Digital Equipment Corp. - Colorado Springs, CO.
Lines: 32

In article <2095@compugen.>, john@compugen. (John Beaudin) writes:
> Something along the lines of Raxco's Rabbit, or DiskKeeper, or Squeezpak.

	ULTRIX(+) uses the Berkeley Fast File System [1] which
	is in a way is very resistant to fragmentation.  Of
	course "very resistant" to fragmentation doesn't mean
	that it can't happen.  A problem I have considered from 
	time to time is how to determine whether a file system
	is badly enough fragmented to warrant trying to clean
	it up.  It is not only a matter of having a file with
	blocks scattered all over, also one of having FILES
	scattered all over and the access patterns of the I/O
	to those files.

	It has been shown that frequently accessed file systems
	should live towards the middle of a disk to get the best
	access times.  I would guess that if you could determine
	which files are the most frequently accessed that you
	should arrange for them to live closest to the center.

	A defragmenter for the FFS wouldn't isn't a "simple" matter
	of compacting all the blocks of a file into one nice little
	area, but it is an interesting problem if it exists.

	[1] - A Fast File System for UNIX*, revised July 27 1983
	Marshall Kirk McKusick, William N. Joy, Samuel J. Leffler,
	Robert S. Fabry.

	(*) UNIX is a trademark of AT&T.
	(+) ULTRIX is a trademark of Digital Equipment Corporation.
-- 
Alan Rollow				alan@nabeth.enet.dec.com