From owner-freebsd-hackers Fri Jun 13 11:43:55 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.5/8.8.5) id LAA12969 for hackers-outgoing; Fri, 13 Jun 1997 11:43:55 -0700 (PDT) Received: from isbalham.ist.co.uk ([192.31.26.1]) by hub.freebsd.org (8.8.5/8.8.5) with ESMTP id LAA12964 for ; Fri, 13 Jun 1997 11:43:49 -0700 (PDT) Received: from gid.co.uk (uucp@localhost) by isbalham.ist.co.uk (8.8.4/8.8.4) with UUCP id TAA07387; Fri, 13 Jun 1997 19:14:34 +0100 (BST) Received: from [194.32.164.2] by seagoon.gid.co.uk; Fri, 13 Jun 1997 19:12:47 +0100 X-Sender: rb@194.32.164.1 Message-Id: In-Reply-To: <199706131634.JAA11079@phaeton.artisoft.com> References: <19970613000752.38538@keltia.freenix.fr> from "Ollivier Robert" at Jun 13, 97 00:07:52 am Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Date: Fri, 13 Jun 1997 19:09:27 +0100 To: Terry Lambert From: Bob Bishop Subject: Re: dump/restore with compression, roberto@keltia.freenix.fr (Ollivier Robert) Cc: freebsd-hackers@FreeBSD.ORG Sender: owner-hackers@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk At 17:34 +0100 13/6/97, Terry Lambert wrote: >> I'd never use any compression -- except hardware-based like DAT's -- >> because you can't recover much if your tape have a problem... I'm against >> compressed file systems for that very reason too. > >This depends on the implementation. A correct implementation will >use block compression rather than file compression or driver level >disk compression to limit the possibility of damage. > >Block compression also has the advantage that the compression tables >are highly sensitive to the type of data, so you don't end up >compressing a region with a suboptimal table. You still get the phenomenon that I usually describe as 'uncompressing the error' - your physical block contains more information when it's compressed, so you lose more than in the uncompressed case even if you can recover. -- Bob Bishop (0118) 977 4017 international code +44 118 rb@gid.co.uk fax (0118) 989 4254 between 0800 and 1800 UK