Re: WD20EARS (4KB sector size) lost Luks header after reboot

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> Hi,
>
> On Tue, Sep 14, 2010 at 06:55:36PM +0200, Ma Begaj wrote:
>> Hi,
>>
>>
>> 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.
>
> That would be one of the 2kB sector drives...

you mean 4kb?

>
>> I already read a few articles how should I format this "special"
>> drive, and I did it like this:
>> http://ubuntuforums.org/showthread.php?t=1456251
>>
>> 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:
>
> Not good.
>
>> fdisk output:
>> --------------
>> root@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
>
> You did create one large partition?

yes just one filling whole disk.


>
> What is the output of "fdisk -lu /dev/sdm1"?
>

root@road:/dev/disk/by-uuid#  fdisk -lu /dev/sdm1

Disk /dev/sdm: 2000.3 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders, total 3907029168 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sdm1              64  3907029167  1953514552   83  Linux

Well, it looks good.



>
>> --------------
>>
>> "Start" is 1 instead of 64.... pretty strange because I set it to 64
>> when I was making this partition.
>
> You set it to 64 sectors. The 1 is a cylinder. You cannto see in this
> view where exactly the partition starts. Use the -u option to fdisk.

Good to know. Thanks.



>
>>
>> luksOpen does not work and luksDump/isLuks reported that /dev/sdm1 is
>> not luks partition.
>
> Interesting.
>
>> I have cryptsetup 1.0.5 on my server.
>
> Aehm, that is hiostoric. Please try with the current one,
> which would be 1.1.3.

Right now before continuing with the rest? I have 3 other luks
partitions on this machine. Should I expect some hiccups?

I am planning to upgrade whole system in the next week and
if possible I will wait until than.



>
>> 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?
>
> I think not, but I am not sure. Before trying that, lets figure
> out whether this is simply an offset issue. Can you look
> through the start of the disk and give the offset where the
> "LUKS" string is exactly?
>
> Something like this should do the trick:
>
> hd /dev/sdm | grep LUKS

"hd"? I don't have hd command on my server.

but I found the position with with dd and vi:

dd if=/dev/sdm of=/tmp/sdm bs=32256 count=1 obs=10240 skip=1


this gives me LUKS on the beginning of /tmp/sdm so offset should be 32256:

LUKSº¾^@^Aaes^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@cbc-essiv:sha256^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@sha1^@^@^@^@^@^@^@^@^@^
   @^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^D^H^@^@^@^Pq^W:<93>CEÚñè©äkÛ)ÍQlÉ<8f>¦ç0à<9b>m^Yr
¡^E


and like this:
root@road:/dev/disk/by-uuid#  dd if=/dev/sdm of=/tmp/sdm bs=1024000 count=1
1+0 records in
1+0 records out
1024000 bytes (1.0 MB) copied, 0.0327064 s, 31.3 MB/s
root@road:/dev/disk/by-uuid#  grep -ob --binary-files=text LUKS /tmp/sdm
32256:LUKS

or grep directly on /dev/sdm

[ 32256 ] should be offset.


What should I do with this?

>
>> fdisk reports "start" on sector 1 instead of 64, which means that
>> something there went wrong.
>
> No, see above.
>
>> 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?
>
> See the FAQ. If you back up the first 100MB, you are on the safe side.
>

root@road:/dev/disk/by-uuid#  dd if=/dev/sdm of=/root/sdm.iso
bs=1024000 count=100
100+0 records in
100+0 records out
102400000 bytes (102 MB) copied, 3.01704 s, 33.9 MB/s


>>
>> 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
>
> Half a pound (500g) of 'b' though a 10 milli-bit connection?
> Sounds like a pain (yes, capitalization can carry meaning).

;-). believe me even 10[M]b is pretty slow if you have to copy 500[GB].

Thanks

M.
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