[dm-crypt] Encrypted Btrfs RAID1

Arno Wagner arno at wagner.name
Thu Sep 12 01:19:44 CEST 2013

On Wed, Sep 11, 2013 at 10:39:13PM +0200, ax487 wrote:
> On 11.09.2013 20:24, Arno Wagner wrote:
> > On Wed, Sep 11, 2013 at 08:13:12PM +0200, ax487 wrote:
> >> Hello all,
> >>
> >> I have been using LUKS for quite some time now to encrypt block devices.
> >> Up to now I have always used the setup RAID1 -> Encryption -> LVM2 ->
> >> filesystems.
> >> Now however I want to create an encrypted Btrfs RAID1. The problem is
> >> that a RAID based on Btrfs is not based on block devices. What I would
> >> need is to encrypt two different partitions and then use their decrypted
> >> counterparts as basis for the RAID. The problem is that I really don't
> >> want to add my pass phrase multiple times and I don't like key files. I
> >> realize that the 'reuse key' problem is a long standing issue:
> >>
> >> https://bbs.archlinux.org/viewtopic.php?id=117152
> >> https://bugzilla.redhat.com/show_bug.cgi?id=446567
> >> https://www.martineve.com/2012/11/02/luks-encrypting-multiple-partitions-on-debianubuntu-with-a-single-passphrase/
> >>
> >> However I did not find a solution anywhere.
> >> Could you tell me how to setup my system to make things work the way I
> >> intend to?
> > 
> > Easy answer: Don't use Btrfs as long as it is not finished (i.e.
> > does not implement encryption). If these people think they can 
> > integrate multiple storage layers, they should at least have the
> > most common in there and that does include encryption.
> Well, I think that Btrfs is ready for a production system. 

Then why are you complaining about its missing features?

> The
> filesystem-based approach to a RAID1 offers some advantages, as does
> Btrfs in general. Also, as I have pointed out, people seem to want
> reusable keys as a feature. If Btrfs becomes the new standard filesystem
> on linux there will probably be some more requests. I might be wrong,
> but I assumed that reusable keys would be a feature not too difficult to
> implement, most certainly much less difficult than for the Btrfs
> developers to implement disk encryption from scratch.
> > 
> > More complicated answer: There is no pre-packaged solution.
> > You could do different things, e.g. make one parition LUKS
> > and the other plain dm-crypt with a key derived somehow from 
> > the LUKS master key.
> I don't know how much you know about what a RAID1 is, but that approach
> pretty much defeats the entire purpose of it...

I very much know what RAID1 is, I just assume you are not 
stupid enough to run a LUKS partition without header backup....

True, if you lose the disk on start-up, then the RAID1 will
not come up, but if you lose it while running, you get
the standard RAID1 redundancy.

Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
There are two ways of constructing a software design: One way is to make it
so simple that there are obviously no deficiencies, and the other way is to
make it so complicated that there are no obvious deficiencies. The first
method is far more difficult.  --Tony Hoare

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