Date: Fri, 13 Jun 1997 19:09:27 +0100 From: Bob Bishop <rb@gid.co.uk> To: Terry Lambert <terry@lambert.org> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: dump/restore with compression, roberto@keltia.freenix.fr (Ollivier Robert) Message-ID: <l0302090eafc73c3cff85@[194.32.164.2]> 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
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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
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