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Date:      Wed, 26 Jan 2011 01:22:17 -0600 (CST)
From:      Scott Bennett <bennett@cs.niu.edu>
To:        freebsd-questions@freebsd.org
Subject:   REPOST:  Re:  help requested in fixing disk label mistake
Message-ID:  <201101260722.p0Q7MHPR028756@mp.cs.niu.edu>

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     A few days ago, I posted here regarding damage resulting from a typing
error and, a few minutes later, posted a followup to correct an error in my
description of the problem.  Thus far I've gotten no responses.  In case the
lack of response is simply due to the message having gotten lost in the flow,
I'm reposting it below.  I hope that someone who is more familiar with the
details of bsdlabels and glabels can help me understand how to correct the
problem because I'm loath at this point to embark upon an ill-informed trial-
and-error experimentation program to recover label and file system(s).

					Scott
     ............................repost follows.........................
     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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