[dm-crypt] Encrypted Raid1 or Raid 1 of encrypted devices?

[Laurence Darby <ldarby@tuffmail.com>]

Hello,

I have 2 disks currently as a RAID1, and want to encrypt it.  I've
done several tests with loopback devices, and found that I can either
create a raid1 with the raw devices, and then encrypt the /dev/md
device, eg:

losetup /dev/loop1 /tmp/a
losetup /dev/loop2 /tmp/b

mdadm --create /dev/md3 --level=1 /dev/loop1 /dev/loop2 --raid-devices=2

cryptsetup luksFormat /dev/md3
cryptsetup luksOpen /dev/md3 md3


or instead encrypt each device, and then make the 2 encrypted devices
into a raid, eg:

losetup /dev/loop3 /tmp/c
losetup /dev/loop4 /tmp/d

cryptsetup luksFormat /dev/loop3
cryptsetup luksFormat /dev/loop4

cryptsetup luksOpen /dev/loop3 data3
cryptsetup luksOpen /dev/loop4 data4

mdadm --create /dev/md4 --level=1 /dev/mapper/data3 /dev/mapper/data4
--raid-devices=2


Is there a recommended way to do this?

I've read the FAQ, especially the part about bad RAM, how single bit
flip errors get amplified - would that mean encrypting each disk
separately is safer, because a bit flip error would be only be copied
to only one device instead of both?  If that happened and a
verification test spotted it, I could remove each device in turn to
find which has the corruption, and repair it.  I am planning on running
the full set of RAM tests anyway.  Is there any reason not to encrypt
each device separately, or any other general advice here?

Thanks,
Laurence