From owner-freebsd-hackers@FreeBSD.ORG  Thu Jan 12 17:56:34 2006
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To: Ivan Voras <ivoras@fer.hr>
In-reply-to: Your message of "Thu, 12 Jan 2006 18:48:20 +0100."
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Date: Thu, 12 Jan 2006 09:56:13 -0800
From: Bakul Shah <bakul@BitBlocks.com>
Cc: freebsd-hackers@freebsd.org
Subject: Re: increasing dd disk to disk transfer rate 
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> Bakul Shah wrote:
> >>In the last episode (Jan 12), Christoph Kukulies said:
> 
> >>dd if=/dev/ad2 conv=noerror,sync bs=64k | dd of=/dev/ad3 bs=64k
> > 
> > 
> > So now on the new disk he has files with random blocks of
> > zeroes and *no* error indication of which files are so
> > trashed.  This is asking for trouble.  Silent erros are
> > worse.
> > 
> > He ought to do a file level copy, not disk level copy on
> > unix.  That way he knows *which* files are trashed and can do
> 
> The problem is, FreeBSD panics when it encounters bad sectors in 
> filesystem metadata. I had the same situation ~a month ago and gave up, 
> restoring from old backups. It will also probably panic on corrupted or 
> zeroed metadata, but at least it's on a readable disk...

Good point.  Would fsdb help?  If not someone ought to extend it.