Re: [Fwd: Re: Missing superblock on one of the raid devices on raid 0 with 1.2 metadata]

[Phil Turmel <philip@turmel.org>]

Hi Ivan,

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

[trim /]

> 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.

> 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.

Phil