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

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.

NeilBrown