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From: NU070156%NDSUVM1.BITNET@wiscvm.wisc.edu (Glen Overby)
Newsgroups: comp.os.minix
Subject: Re: bad blocks on hard disk
Message-ID: <484@louie.udel.EDU>
Date: Fri, 4-Sep-87 14:24:19 EDT
Article-I.D.: louie.484
Posted: Fri Sep  4 14:24:19 1987
Date-Received: Sat, 5-Sep-87 18:23:14 EDT
Sender: mmdf@udel.EDU
Lines: 22


In his message of 3 Sep 87, Andy Tanenbaum <ast@cs.vu.nl> writes:
> In article <196@turbo.RAY.COM> jim@turbo.RAY.COM (Jim Shaw x8232) writes:
> >...  I have a couple of known bad tracks ...
>
> I believe that the DOS approach to bad tracks is to keep the last couple
> of tracks in reserve, and to have a map that tells which of the regular
> tracks are bad.  It then subsitutes the reserve tracks (or maybe just
> sectors, I am not sure) for the bad ones.

Some hard disk controlers use this technique to "hide" bad tracks from
DOS, but DOS itself has the capability to lock out bad sectors (actually
allocation units). These sectors are what show up as bad sectors when
running 'chkdsk'. The tracks that the controler maps out will be invisible.

The controler mapping should still be invisible to Minix, but an alternate
scheme of locking would also be desireable. Building a 'bad block file'
is an old kludge of Unix's, but it works.

Glen Overby
Bitnet: nu070156@ndsuvm1
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