Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!hao!oddjob!gargoyle!ihnp4!cbosgd!osu-cis!apr!las
From: las@apr.UUCP (Larry Shurr)
Newsgroups: comp.os.minix
Subject: Re: bad blocks on hard disk
Message-ID: <273@apr.UUCP>
Date: Tue, 8-Sep-87 13:10:01 EDT
Article-I.D.: apr.273
Posted: Tue Sep  8 13:10:01 1987
Date-Received: Wed, 9-Sep-87 06:56:47 EDT
References: <196@turbo.RAY.COM> <489@ast.cs.vu.nl>
Reply-To: las@apr.UUCP (Larry Shurr)
Organization: APR, Columbus, OH
Lines: 37

In article <489@ast.cs.vu.nl> 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.
>
This approach to bad track handling is generally a function of the controller
in conjunction with the formatting software (low-level format).  In this
scheme, the controller provides a "format-bad-track" function which writes
a bad-track header in place of the regular sector headers which tells the
controller "I'm a bad track - this track remapped to xxxx" where xxxx is the
physical address of another track which takes the place of the bad track.
The allocation scheme for replacement tracks is performed by the format
software although there are generally restrictions imposed by the controller
such as the replacement track must be on the same surface as the bad track.
You can get away with this most times because a bad track is generally not
completely unreadable/writable.

Now before you flame me, there's no way I can guarantee that all controllers
support this, nor can I guarantee that all low-level format software supports
this feature if it is available.  I just know that this is the way it worked
with the controller for which I wrote formatting software for the TI Pro.

Now the way DOS "handles" this is that it doesn't handle bad tracks.  The
FORMAT program handles unreadable sectors by marking the clusters which
contain them as "unavailable" in the FAT.  DOS then handles them by not
using the affected clusters.

regards, Larry
-- 
"The only thing worse than being talked about is not being talked about."
- Oscar Wilde, James Whistler or George Bernard Shaw depending on who you ask
Name: Larry A. Shurr
Addr: cbatt!osu-eddie!apr!las (preferred, alternates: {cbosgd,ihnp4}!cbcp1!las)