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From: wert@Navajo.UUCP
Newsgroups: net.micro.mac
Subject: Re: macintosh file system and disk layout questions.
Message-ID: <545@Navajo.ARPA>
Date: Wed, 30-Apr-86 20:14:50 EDT
Article-I.D.: Navajo.545
Posted: Wed Apr 30 20:14:50 1986
Date-Received: Sat, 3-May-86 21:09:18 EDT
References: <429@geowhiz.UUCP> <430@geowhiz.UUCP>
Reply-To: wert@Navajo.UUCP (Scott Comer)
Distribution: net
Organization: Stanford University
Lines: 21

On almost any disk drive ever used, there are these things called
address marks and data marks. The address marks are used by the
drive to verify that it has positioned correctly before reading
and writing, and the data marks have stuff like CRC correction
codes, etc. This is not the same as the file tags which MFS (and
maybe HFS) puts out there. When the drive says that it cannot
find the sector, it probably means that the address marks have
been trash. Once that happens, that sector is gone for good.

There might be something like an extended write (I have never
used fedit, so I don't know) that would let you write the
sector over with zeros or something, but short of that, you
will have to reformat the disk to get it back.

Plan: edit the sector out of the file that references it, by
diddling the volume allocation block map. Be very carful. Allocate
some other sector, fill it with zeros, and put it in the bad sectors
place. Now, copy all the files to another disk, and reformat that
one. Voila! Everything is ok, except that you lost a sector. Too bad.

scott out.