From owner-freebsd-hackers  Wed May  9 22:10:32 2001
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From: Luigi Rizzo <luigi@info.iet.unipi.it>
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Subject: Re: fd driver hacking to recover data
In-Reply-To: <Pine.BSF.4.21.0105092153220.3063-100000@thought.adamantsys.com>
 from "Brian W. Buchanan" at "May 9, 2001 10:04:34 pm"
To: "Brian W. Buchanan" <brian@CSUA.Berkeley.EDU>
Date: Thu, 10 May 2001 07:07:53 +0200 (CEST)
Cc: hackers@FreeBSD.ORG
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> I have a bunch of old floppy disks with some text files I'd like to
> recover.  Many of them have errors and are unreadable past a certain point
> in the disk.  Others I can't read from at all.
> 
> The ones I can't read, period, are all 1.44MB-size floppies.  I've tried
> dd'ing from /dev/fd0c, /dev/fd0.1440, etc., but exits with "Input/Output
> Error" before copying anything.

i think you can try dd from the raw device (/dev/rfd) using the "iseek"
or "skip" option to jump over the missing sectors.
Alternatively, you can use "conv=noerror,sync" to keep reading
after errors (the bad blocks are NUL-filled)

	cheers
	luigi

> The kernel prints:
> 
> fd0c: hard error reading fsbn 0 of 0-31 (ST0 40<abnrml> ST1 1<no_am> ST2 0
> cyl 0 hd 0 sec 1)
> 
> 
> I've been more successful reading 720K floppies from /dev/fd0.720, but
> many of them have errors that stop dd in its tracks, yielding another
> Input/Output error.
> 
> The kernel prints:
> 
> fd0c: hard error reading fsbn 1503 of 1488-1503 (ST0 44<abnrml,top_head>
> ST1 20<bad_crc> ST2 20<bad_crc> cyl 41 hd 1 sec 10)
> 
> 
> Since the files on the disks are just text, all I want to do is to be able
> to extract as many of the bits on the disk as possible, even if some of
> the bits are wrong, and then run strings over it and sort out the
> content.  I've looked at the floppy driver source and it seems to be
> incredibly low-level, i.e. it turns the drive motor on and off, even.  Can
> someone familiar with the driver give me some pointers as to what I'd have
> to modify to let it 1) read those 1.44MB disks, and 2) tolerate data
> errors?
> 
> Thanks,
> 
> Brian
> 
> -- 
> Brian Buchanan                                     brian@CSUA.Berkeley.EDU
> --------------------------------------------------------------------------
> FreeBSD - The Power to Serve!                       http://www.freebsd.org
> 
> 
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