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Date: Mon, 11 Nov 2013 08:19:57 -0700 (MST)
From: Warren Block <wblock@wonkity.com>
To: Erich Dollansky <erich@alogt.com>
Subject: Re: documentation of GEOM data structures needed
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On Mon, 11 Nov 2013, Erich Dollansky wrote:

> I would need a documentation of the GEOM data structure. A disk got
> damages in a strange way during the process of backing up data. It was
> partitioned with gpart as all my disks using the MBR schema. When
> creating the backup, the system crashed. The disk was not usable
> anymore. I found out that the MBR was overwritten before the backup was
> started while the beginning of the first partition seems to be ok.

MBR does not have any specific GEOM structure.  It's just a standard 
MBR: http://en.wikipedia.org/wiki/Master_boot_record

See the end of the mdconfig(8) man page for an example of using it and 
gnop(8) to skip over an arbitrary length of data at the start of a disk.

With that and file -s, you can attempt to find mountable filesystems on 
the whole disk.  A script would be the fastest way.  The first one 
should be relatively easy.  After that, guessing approximate locations 
would speed it up a lot.