On 15/03/13 16:52, Phil Turmel wrote:

Hi Ivan,

On 03/15/2013 12:29 PM, Benjamin ESTRABAUD wrote:

[trim /]

quoted

The fact that you have the position of all the other drives from the
array is good. Now we want the last drive's superblock to be written.
Since we know the position of all the drives, and assuming you know the
*exact* arguments passed to mdadm when you first created your raid0
(correct metadata version, chunk size, etc. (most can be found in the
existing superblocks), you could call "mdadm --create " with the same
version of mdadm and MD used when creating the array initially, the same
options and arguments, and *very important* the drives in the same
order, which I believe to be: /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1
(according to the info above).

This will create a new array, but since you are recreating the same
*exact* array, the existing data should be there and available untouched.

This is all correct, and is the correct next step.

quoted

However, as a word of warning, many things can go wrong this this
command: If you were to recreate the array slightly differently and
start overwriting your array you would destroy the data on it. The fact
that it is a RAID0 is good since creating a new array won't start a
resync that could be fatal should you have made a mistake providing the
arguments for the recreation. So the above should be generally safe,
provided you keep a copy of the information you gave us above and match
the "create" arguments perfectly.

You can check your work by re-issuing the "mdadm -E" commands after
re-creating the array.  The data offset and chunk size must match the
originals.

If they do, then you can mount the filesystem.

One thing though: Note that your array will be recreated with a new 
array UUID, creation time, and possibly other attributes (although none 
related to the contents of the RAID, the data), should you rely on the 
RAID UUID for anything in particular. It is highly unlikely but just to 
let you know in case you run into troubles with some applications 
depending on the RAID uuid.

Phil