Neil Brown wrote:

On Mon, 25 Jan 2010 10:52:21 +0100
Andre Noll [off-list ref] wrote:

  

quoted

On 15:09, Jim Paris wrote:

    

quoted

I guess the only way to be fully safe with the current approach is to
do a zero-superblock over and over until it complains.
      

mdadm --zero-superblock tries to guess the location of the superblock.
If more than one superblock is found, the one with the latest creation
time is being zeroed. So yes, the method you describe works and I think
it is the most reliable way to remove all superblocks of a device.

Maybe we could teach mdadm --zero-superblock to honor the --metadata=x
option which would zero-out the region of the device where the
version-x superblock is located.
    

Latest mdadm has this feature.
And if --metadata= isn't given, it repeatedly trying to find and zero a
superblock until no more superblocks can be found.
  

That would be potentially a bad thing, people do run things like RAID1+5 
and might want to clear on block and save the other, still possibly part 
of a running array, one. I'm not sure that's a safe default behavior.

-- 
Bill Davidsen [off-list ref]
  "We can't solve today's problems by using the same thinking we
   used in creating them." - Einstein