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Date: Sun, 04 Jul 2010 15:57:45 +0200
From: Dimitry Andric <dimitry@andric.com>
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To: Daniel O'Connor <doconnor@gsoft.com.au>
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Cc: FreeBSD Stable <freebsd-stable@freebsd.org>
Subject: Re: GEOM/bsdlabel regression in 8.x?
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On 2010-07-04 14:24, Daniel O'Connor wrote:
...
> mkdir /mnt/test
> mount /dev/md0s1a /mnt/test
> bsdlabel -e /dev/md0s1
> 
> Then you get..
> "bsdlabel: Class not found"

First unmount /dev/md0s1a, or the device /dev/md0s1 will be in use, and
opening it for read/write (as bsdlabel probably does) will fail.

Alternatively, you can turn on the "footshooting" debug flag in geom:

     Protection mechanisms in the geom(4) subsystem might prevent boot0cfg
     from being able to update the MBR on a mounted disk.  Instructions for
     temporarily disabling these protection mechanisms can be found in the
     geom(4) manpage. Specifically, do a

           sysctl kern.geom.debugflags=0x10

     to allow writing to the MBR, and restore it to 0 afterwards.

and try again.  This may not work as expected though. :)