[dm-crypt] can't open luks device after raid 5 rebuild

Arno Wagner arno at wagner.name
Sun Apr 8 22:28:23 CEST 2012

On Sun, Apr 08, 2012 at 05:07:28PM -0300, Salatiel Filho wrote:
> On Sun, Apr 8, 2012 at 14:09, Heinz Diehl <htd at fancy-poultry.org> wrote:
> > On 08.04.2012, artificial11000 wrote:
> >
> >> ?mdadm --create --level=5 -n 3 /dev/md127 /dev/sdb /dev/sdc /dev/sdd
> > ? ? ? ? ---------
> >
> > Seems your data is gone, forever. You created a new raid manually,
> > which means that you deleted all your previous data.
> >
> > You have a backup, do you?
> >
> > _______________________________________________
> > dm-crypt mailing list
> > dm-crypt at saout.de
> > http://www.saout.de/mailman/listinfo/dm-crypt
> I disagree. I got some missing superblock sometime in the past while
> assembling the array. Recreated it using mdadm -C with the same
> parameters for the raid-level and raid-devices and it did not touch my
> encrypted data. I was able to mount just fine after that. I always
> thought that mdadm would touch only their own superblock when
> creating. 

No, it recreates the parity stripes. It has to, otherwise RAID consistency
checks would fail. If, for any reason, drive/device 
order or stripe size is diferent, this will scramble your data. 
The data is still there unless you write to the array, see my other 
answer. It also overwrites the RAID superblocks.

If everything is the same, the original data will be there though,
because the new parity stripes are exactly at the same positions 
on the same disks as the old ones and created from the same 
non-parity stripes.

> Though at that time i had a degraded  array and my array is
> built on partitions , not the whole disk.

On a degraded array, you should always only (re-)add the missing 
device or a replacement.

Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno at wagner.name 
GnuPG:  ID: 1E25338F  FP: 0C30 5782 9D93 F785 E79C  0296 797F 6B50 1E25 338F
One of the painful things about our time is that those who feel certainty 
are stupid, and those with any imagination and understanding are filled 
with doubt and indecision. -- Bertrand Russell 

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