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Path: utzoo!watmath!clyde!bonnie!akgua!gatech!seismo!mcvax!vu44!botter!ark!gijs
From: gijs@ark.UUCP (Gijs Mos)
Newsgroups: net.micro.mac
Subject: Re: A Disk Recovery Tale
Message-ID: <600@ark.UUCP>
Date: Sun, 24-Nov-85 07:39:33 EST
Article-I.D.: ark.600
Posted: Sun Nov 24 07:39:33 1985
Date-Received: Mon, 25-Nov-85 08:07:34 EST
References: <8511161155.AA10811@kim> <2177@reed.UUCP>
Reply-To: gijs@ark.UUCP (Gijs Mos)
Organization: VU Informatica, Amsterdam
Lines: 15

>> [...] Somehow, miraculously,
>> the directory blocks on my "trashed" disk were fixed as they were copied
>> to the new disk.  They couldn't be read by fedit nor by the Mac's disk insert
>> handler, but they could be copied.  How can this be?  You tell me.

The explanation is simple. The errors on your old disk must have been caused 
by bad address marks or the like. If your copy program copies the good 
sectors to a newly formatted disk all address marks will be ok on the new
disk. The sectors on the new disk corrosponding to the bad sectors on the
old disk will not contain valid data however. Fortunately there is a lot of
redundancy in the Mac's file system. If the bad block used to be in the
directory the Mac rebuilds the directory. 

Gijs
{seismo,decvax,philabs}!mcvax!vu44!gijs