Yet another RAID admin question

[Hendrik Boom <hendrik@topoi.pooq.com>]

I have successfully identified and decommissioned a failing RAID 
partition -- my RAID1 was then running properly with only one of its two 
twinned partitions.  Every timr I booted, I got a message complaining 
that it was deficient.  The drive with the failing partition was indeed 
defective, and has been physically removed from the computer. and 
replaced with two new ones, which have been tested by exhaustive read-
write testing.

I've created partitions for the RAID on the new drivew, and successfully 
added them.

The new drives are three times as big as the old ones.  I'd like to drop 
the remaining old one from the RAID setup now, so I can triple the size 
of the RAID.

Now presumably I can use mdadm to software-fail it, or to remove it, or 
something like that.

But I understand these partitions are marked in some way to identify them 
as RAID members, and that these marks are used at boot time to asssemble 
the RAID.

What do I have to do to make sure that after I have removed the old 
member it is never again recognised as a RAID member?

-- hendrik