Path: utzoo!attcan!uunet!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Possibilities for speeding/expanding standard floppies
Message-ID: <4733@cbmvax.UUCP>
Date: 14 Sep 88 23:56:12 GMT
References: <2619@sugar.uu.net>
Organization: Commodore Technology, West Chester, PA
Lines: 37

in article <2619@sugar.uu.net>, peter@sugar.uu.net (Peter da Silva) says:
> In article <4705@cbmvax.UUCP>, daveh@cbmvax.UUCP (Dave Haynie) writes:
>> two.  This level of recover really doesn't belong in the trackdisk.device.

> Weren't you just telling me that the device should present an error-free
> disk to the file system? That was the rationale behind not putting error
> correcting code there, remember. Where should this code be, then? The drive?

I like the idea of the device handling the error checking/correcting as much
as possible.  But it's not always possible in the context of a device driver.
For example, you yank out a floppy in the midst of a write and reset your
machine.  Now plug the floppy back in.  On that track that got blasted, there
are probably at least two sectors that are totally trashed; chopped in half
probably.  There's a really good chance that there are also some sectors that
aren't there at all, and some that are there in duplicate.  Remember, trackdisk
as used isn't synced at all.

So how does trackdisk give me back those sectors that are still readable?  As
far as it knows, both versions of sector 5 are equally valid.  Without 
knowledge of the filesystem you happen to be using, how is the device to
choose between the two.  Similarly, the File System doesn't know about the
low level aspects of each individual device driver, so it's not qualified
to solve the problem.  

I can think of two appropriate solutions.  First, the device driver could have
the capability to pass up several versions of a particular sector if it finds
multiple sectors, and let the file system try to determine which is the right
one.  The other solution is to tell the user he's got a bad disk, and let him
go and get a utility specifically designed to recover bad disks.  That's what
we do now.  I think's a decent way to solve the problem at hand.

> 		Peter da Silva  `-_-'  peter@sugar.uu.net
> 		 Have you hugged  U  your wolf today?
-- 
Dave Haynie  "The 32 Bit Guy"     Commodore-Amiga  "The Crew That Never Rests"
   {ihnp4|uunet|rutgers}!cbmvax!daveh      PLINK: D-DAVE H     BIX: hazy
		"I can't relax, 'cause I'm a Boinger!"