[gentoo-user] Fileserver with Raid + Crypto + BtrFS

[Ralf <ralf+gentoo@ramses-pyramidenbau.de>]

Hi,

at the moment i'm running a gentoo box as fileserver, the setup is as
follows:

 -----------------------------------
|               Ext4                |
 -----------------------------------
                  ^
                  |
 -----------------------------------
|               LUKS                |
 -----------------------------------
                  ^
                  |
 -----------------------------------
|            MD Raid 10             |
 -----------------------------------
   ^         ^         ^         ^
   |         |         |         |
 -----     -----     -----     -----
| hd0 |   | hd1 |   | hd2 |   | hd3 |
 -----     -----     -----     -----


Besides other features, I'd like to have a snapshot functionality, and I
don't want to introduce an additional layer by using LVM. So I'm
thinking about to migrate to Btrfs.

Btrfs supports Raid10 but no block-crypto.

If I would use a HD->MD Raid->Luks->Btrfs stack, I don't benefit from
the Raid implementation of Btrfs.
If I would use a HD->Luks->Btrfs stack, then I would have to use four
different LUKS devices, which results in four individual encryptions
(and I don't have AES-NI, so this would be a tremendous slowdown).

What would be the best way to have a Raid 10 together with a encrypted
Btrfs?

--

Besides that I would have to live-migrate the Raid10 as I don't have any
spare hdd to cache the data. So I would have to degrade my Raid10.
Is it possible to create a degraded Btrfs?

Please don't tell me that this is insanely dangerous, I know it is ;-)

Cheers
  Ralf