[dm-crypt] WD20EARS (4KB sector size) lost Luks header after reboot

Ma Begaj derliebegott at gmail.com
Tue Sep 14 18:55:36 CEST 2010


I got a new HDD a few days ago and I put it in an external case and connected
it over USB with my home server. It is a 2000GB WD disk,  WD20EARS.

I already read a few articles how should I format this "special"
drive, and I did it like this:

I set the partition to begin on sector 64 (instead of 63), run
luksFormat, run luksOpen,
created XFS and copied my files on this disk. I umounted it later and
I rebooted
the server today.

First thing I noticed is that disk/paritions are not visible in
/dev/disk/by-uuid/ although
/dev/sdm and /dev/sdm1 are available. fdisk also does not look same as before:

fdisk output:
root at road:/dev/disk/by-uuid#  fdisk /dev/sdm

The number of cylinders for this disk is set to 243201.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): p

Disk /dev/sdm: 2000.3 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sdm1               1      243202  1953514552   83  Linux


"Start" is 1 instead of 64.... pretty strange because I set it to 64
when I was making this partition.

luksOpen does not work and luksDump/isLuks reported that /dev/sdm1 is
not luks partition.

I have cryptsetup 1.0.5 on my server.

There are two questions for me here:
1. I have luksDump of /dev/sdm1 before this happened. Can I use
luksDump ouput  to
recover/overwrite Luks partition?

fdisk reports "start" on sector 1 instead of 64, which means that
something there went wrong.
Or not? Ideas? If I can use luksDump to recover luks-header should the
partition table maybe be
rewritten beginning with sector 64 before I recreate luks header.

2. How all this could happen?

I would be very happy to experiment with this, to repeat all the steps
to recreat the situation
 if I know that I am able to recover my partition. Any ideas before I
start to play with this?
How much of the partition header should I backup before starting with
all of this?

Thanks a lot for any advice.


p.s. I have all the data but I would like to avoid copying again
because I have to copy everything
(over 500gb) over SSH trough a 10mb connection

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