[CentOS] mdadm syntax

Hi All,
    I am trying to create an MD device.  I am using the command:
/sbin/mdadm --create --a /dev/md12 --level=1 --run --raid-devices=2
/dev/sda12 /dev/sdb12
to create the device, and to dynamically create the device file if needed.
What I want is the device file to be created as /dev/md12, but with the -a
flag it creates it as /dev/md<first unwsed minor number>.

I have tried various options to the -a or --auto, but cannot seem to find
the correct syntax.  From the man page it says:
       -a, --auto{=no,yes,md,mdp,part,p}{NN}
              Instruct mdadm to create the device file if needed, and to
allocate an unused
              minor number.  "yes" or "md" causes a non-partitionable
array  to  be  used.
              "mdp", "part" or "p" causes a partitionable array (2.6 and
later) to be used.
              The argumentment can also come immediately after "-a".  e.g.
"-ap".

Am I doing something wrong, or is there no way to get mdadm to automatically
create a specific device file.

Thanks...
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