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Date:      Sun, 20 Sep 2020 22:55:11 -0700
From:      David Christensen <dpchrist@holgerdanske.com>
To:        freebsd-questions@freebsd.org
Subject:   Re: Create new geli file system using existing key
Message-ID:  <b484587f-93a3-84da-6e4f-3e564ff9bbfd@holgerdanske.com>
In-Reply-To: <CAN6yY1vShj8DLnSNzD5id3TE1-bjAKCFMO0Fg63JNmWvWBnXRg@mail.gmail.com>
References:  <CAN6yY1uE-gfijR8n8+A0k6ufB=6EYEc6RbgbgpXj+V=80GOHPA@mail.gmail.com> <fef7fd7a-2f6c-0d09-e1e7-8bcd1589ed9e@holgerdanske.com> <CAN6yY1vShj8DLnSNzD5id3TE1-bjAKCFMO0Fg63JNmWvWBnXRg@mail.gmail.com>

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On 2020-09-20 12:44, Kevin Oberman wrote:
> After thinking about this a bit longer, it's not really hard to do what I
> need to do using the resize command. More significantly, I really don't
> need to do this.
> 
> Quick explanation of why this would be "helpful". I backup using rsync to a
> USB disk. I simply attach and mount the USB partition and fire up the
> synchronization (with a number of options and exceptions). It's convenient
> to have a single key file on thumb drive (geli attach -d
> -k/media/keys/FILENAME) with that command as an alias so I just type
> "gattach /dev/gpt/PARTITION". Hey, I'm lazy. A keystroke saved is a
> keystroke earned!
> 
> I plan to change the alias to a very short script to pick the correct key
> for the operating and backup partitions. What I type won't change.

So, your backup media is USB hard disk drives, each drive has a GELI 
provider (containing a filesystem), the GELI keyfile is on a USB flash 
drive, and you have a script "gattach" that attaches the backup disk 
GELI providers using the keyfile (?).


I do not believe you need (or want) to have identical GELI metadata on 
the USB hard disk drives.  I believe you just need to specify the same 
keyfile when you create each GELI provider.


Also, I also do not believe you need to resize.  When you provision a 
device as backup media, partition it to use all or most of the available 
space, create a GELI provider using the keyfile on the USB flash drive 
and a passphrase you have memorized, attach the GELI provider, and 
create a filesystem.  Done this way, connecting multiple backup drives, 
attaching multiple backup GELI containers, and mounting multiple backup 
filesystems at the same time should not be a problem.


I presume you have (encrypted) backups of the keyfile (!).


Alternatively, GELI has two "slots" and you can put a (strong) 
passphrase alone into the second slot.  That way, if you lose everything 
except one backup drive and the second passphrase, you can still recover.


David



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