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Date:      Sat, 22 Jan 2011 22:22:01 -0600 (CST)
From:      Scott Bennett <bennett@cs.niu.edu>
To:        freebsd-questions@freebsd.org
Subject:   Re:  help requested in fixing disk label mistake
Message-ID:  <201101230422.p0N4M14G012454@mp.cs.niu.edu>

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     I just wrote:
>     A couple of days ago, I reorganized the internal hard drive of my machine
>to reclaim space that used to be occupied by another operating system for use
>with my now exclusively FreeBSD system.  I used a stand-alone partition manager
>to edit the slices down to just two slices.  I then attempted to bsdlabel the
>first slice, but made a bit of a slip.  When I should have typed
>
>	bsdlabel -w ad0s1
>
>I actually typed
>
>	bsdlabel -w da0s1
>
>Oops.
>     I went ahead with the work on the internal drive (ad0), and the system
>is up and running fine.  Now I'd like to try to fix the damage done to the
>external drive that I relabeled by mistake.  That drive's layout before the
>damage was done was a single slice, divided into two partitions (da0s1 and
                                                                  ^^^^^
>da0s2), each of which was then glabel'ed.  The moment I rewrote the bsdlabel
 ^^^^^
     Yet another pair of mistakes on my part.  Those should have said da0s1d
and da0s1e.  Sorry for any confusion.
     
>for the first slice by mistake, the two partitions' entries in /dev/label
>vanished, of course.  I checked and discovered that the only external drive
>for which I had not kept backup copies of the bsdlabel information was that
>drive. :-(  Fortunately, the full backups of the file systems that I needed
>to reload onto the internal drive were in the first partition of the external
>drive in question (used to be s1d, now s1a for the time being), so by mounting
>/dev/da0s1a I still had full access to the file system containing the backups.
>     My hypothesis is if I can somehow rewrite a correct bsdlabel for the
>affected slice, that the system will then recognize the glabel metadata for
>the two partitions immediately, and the /dev/label entries will appear right
>away like magic.  Unfortunately, without a backup file of the bsdlabel
>information, I'm unsure how to accomplish that.  Is there some way that I can
>discover the exact size in sectors of the first partition, so that I could
>edit the bsdlabel information and redefine it as two partitions of the correct
>sizes and offsets?  Is there some field in dumpfs(8) output that would give me
>what I need (allowing, of course, for the fact that the first partition
>is actually one sector longer than anything dumpfs(8) would know about due to
>the glabel metadata in the final sector of the partition)?  Or is my hypothesis
>stated above actually incorrect, and if so, why/how?
>     PLEASE send any replies to ME DIRECTLY (or at least Cc: me directly)
>because I receive this list in digest form and am at least a week and a half
>behind on my reading. :-}  Thanks much in advance for any helpful ideas.


                                  Scott Bennett, Comm. ASMELG, CFIAG
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* Internet:       bennett at cs.niu.edu                              *
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