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Date: Wed, 31 Aug 2011 06:11:12 -0700
From: perryh@pluto.rain.com
To: basarevych@gmail.com
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Cc: freebsd-questions@freebsd.org
Subject: Re: Is there way to get filename for specific LBA?
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Ross <basarevych@gmail.com> wrote:

> Aug 31 05:13:24 da kernel: ad6: WARNING - READ_DMA UDMA ICRC error
> (retrying request) LBA=107491647

That message is reporting a problem in communication between the
drive and the controller (or, perhaps, between the controller and
main memory), not a problem reading the media, so the LBA is likely
not all that useful (esp. since, if you got no other messages, the
retry succeeded so no data was lost).

What does

  egrep 'ad[0-9]|ata' /var/run/dmesg.boot

report?

> #  dd if=/dev/ad6 of=/dev/null bs=1m seek=107491647 count=1
> dd: /dev/null: Inappropriate ioctl for device
>
> Another question: why does it fail?

seek= applies to the output file, so it tried to do a seek on
/dev/null :)  You probably wanted skip= (or iseek=).