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Date:      Tue, 25 Jan 2011 10:45:52 +0200
From:      Nikos Vassiliadis <nvass9573@gmx.com>
To:        "J. Porter Clark" <jpc@porterclark.com>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: How to label a GELI device
Message-ID:  <4D3E8DC0.9060605@gmx.com>
In-Reply-To: <20110125014223.GA13385@auricle.charter.net>
References:  <20110125014223.GA13385@auricle.charter.net>

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J. Porter Clark wrote:
> I have an encrypted partition, /dev/da0s1d.  I can use geli
> attach da0s1d and obtain a device /dev/da0s1d.eli, which is a
> UFS filesystem.  All that works just fine.
> 
> I'd like to label /dev/da0s1d so that I don't have to refer to
> the exact drive number, etc., which might change if I reboot
> with a USB stick in the system or whatever.  But glabel puts the
> label in the last sector, which is where GELI stores metadata.

You don't have to worry about this. geli uses the last sector for
its metadata and creates a device with one sector less to its clients.
The original device is 2048 sectors, the device geli provides is 2047
sectors:
> moby# diskinfo /dev/md0 /dev/md0.eli
> /dev/md0        512     1048576 2048    0       0
> /dev/md0.eli    512     1048064 2047    0       0

There is no way for the "internal" GEOM to mess with the "external's"
metadata.

> So, how do I make this work?
> 

glabel apart from the generic device labeling, supports UFS labels which
are *part* of the filesystem, that is, you *don't* have external metadata
living in a sector outside the filesystem. Check tunefs manual page and
specifically the -L option.

HTH, Nikos



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