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It works on Model S as long as the hard drive is formatted correctly (can't remember if it needs FAT32 or whatever) . It even recognizes multiple partitions on the same drive.
I was going to try it when sentry mode actually rolls out. I bought a USB3 to sata adapter and have several small SSDs laying around in the 80 to 160gb range.
I probably would recommend using a mechanical drive. But it might work, just will be a bit slow. I have a bunch of these too.