This is a mod I did to our 2010 (unibody) Mac mini server. I had already removed the drives that came with it and installed one SSD. The other 2nd drive connector is what I used for the esata.

Here is the cable I used:
cooldrives.com/esexcaitolex.html

You will have to cut off the tabs and a little part of the mini drive connector. I epoxed the connectors together since we move this computer around alot but just taping it would probably work fine.

The external drive must be plugged in before booting and is not hot swappable. Maybe there is a way to change this but I don't know it.

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