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From: Luigi Rizzo <luigi@labinfo.iet.unipi.it>
Message-Id: <199602272300.AAA04556@labinfo.iet.unipi.it>
Subject: Re: OK, so what would YOU like to see on that second CD?
To: terry@lambert.org (Terry Lambert)
Date: Wed, 28 Feb 1996 00:00:16 +0100 (MET)
Cc: jfieber@indiana.edu, jerry@border.com, jkh@time.cdrom.com,
        hackers@FreeBSD.ORG
In-Reply-To: <199602272049.NAA05743@phaeton.artisoft.com> from "Terry Lambert" at Feb 27, 96 01:48:58 pm
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> I have some example file compression code for the Heidemann framework;
> John has asked that I not redistribute it.

but the problem is not the compression code, there's plenty of it
out there, and some is even reasonably fast [and often the same
algorithm has been patented several times by different people,
*after* an implementation was made available on the net; I was
reading the comp.compression FAQ the other night and it's full of
this kind of stories! ].  The problem is that compressed blocks
have variable size, and handling them efficiently requires (I
believe) big changes in the device+fs code. Perhaps log-structured
filesystems lend themselves better to this.

> It would be trivial to implement block compression at the device export
> layer in the devie framework I suggested previously.  This is similar

while you can certainly make a compressed device look like a regular
one, I believe some efficiency is lost, and not only because of
compression. The FS layout assumes that adjacent blocks are adjacent
(modulo a few bad sectors). But what on a compressed device ?

	Luigi
====================================================================
Luigi Rizzo                     Dip. di Ingegneria dell'Informazione
email: luigi@iet.unipi.it       Universita' di Pisa
tel: +39-50-568533              via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522              http://www.iet.unipi.it/~luigi/
====================================================================