Need some more MDADM details

Short version: I am using a RAID1 with hotspare and I want to have a nightly DD ran to create a nightly image on a standby drive. All the drives are the same size/manufacture and local. I am getting a issue where the DD is performed properly dd if=/dev/sda (part of the raid) of=/dev/sdd (empty drive not part of the raid) but upon reboot the MDADM tries to add the SDD to the RAID automatically. I have tried setting the AUTO -all within /etc/mdadm.conf however since the drives are DD images it copies over the super block and identifies which confuses the MDADM and adds it to the RAID upon reboot.

Real question: Is there a way to see what drives are "identified" for the RAID? Is that stored elsewhere besides the /etc/mdadm.conf? Is that stored on the partitions on the drive's super block and is read upon mdadm --assemble --scan @ boot?

Disclaimer: I know this is a very particular question and I might need to post this to the MDADM bug report perhaps? Also I am determining the free drive via a comparison of current RAID drives and adding it to a keyfile that will store drive by-id information so that the DD script does not attempt to overwrite the wrong drive. Any input is much appreciated. Thanks!

Versions and outputs

• OS Centos 6.8
• MDADM 3.3.4

http://pastebin.com/1GxUY0BP

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