[dm-crypt] After reboot: "Command failed with code 22: Device /dev/md2 is not a valid LUKS device."

[Jens-Michael Hoffmann <jmho@jmho.de>]

hello,

the LUKS device in question was setup on top of a raid6 (/dev/md2) consisting 
of 6 partitions (1.8TB each).

The LUKS device was created with

cryptsetup --verbose --cipher=aes-xts-plain64 --key-size=256 --verify-
passphrase luksFormat /dev/md2

Then it was opened with (probably, what I could tell from history):

cryptsetup -v create md2_crypt /dev/md2

and a XFS filesystem was created on top of it.

I put some files on the filesystem which all seemed to work.
After the first reboot, the array was assembled correctly, but I could not 
create the crypt mapping anymore:

root@babylon5:~# LANG=C cryptsetup -v --debug isLuks /dev/md2
# cryptsetup 1.4.3 processing "cryptsetup -v --debug isLuks /dev/md2"
# Running command isLuks.
# Allocating crypt device /dev/md2 context.
# Trying to open and read device /dev/md2.
# Initialising device-mapper backend, UDEV is enabled.
# Detected dm-crypt version 1.12.1, dm-ioctl version 4.23.1.
# Trying to load LUKS1 crypt type from device /dev/md2.
# Crypto backend (gcrypt 1.5.0) initialized.
# Reading LUKS header of size 1024 from device /dev/md2
# LUKS header not detected.
Device /dev/md2 is not a valid LUKS device.
# Releasing crypt device /dev/md2 context.
# Releasing device-mapper backend.
Command failed with code 22: Device /dev/md2 is not a valid LUKS device.

The data I put there was not overly important, but still it would be nice if 
it would not be all lost.

Is there anything I can try? (I did not yet try cryptsetup --repair)


kind regards,
Jens-Michael