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Both drives are now inside your MacPro?
You are now booted to a drive that came out of another MacPro?
If you run Disk Utility does it see both drives?
"I am a mortal enemy to arbitrary government and unlimited power. I am naturally very jealous for the rights and liberties of my country, and the least encroachment of those invaluable privileges is apt to make my blood boil."
2013 MacPro, Areca 5026 Thunderbolt RAID, pair of 23 inch Cinema and a LogiTech Anywhere MX laser moose