Yeah, I have just got back tothis after a long time. I am sorry I found it did not work in the end due to multiple issues. TheM3 cannot be booted from SATA directly, even just mapping usr and var over using fstab runs into problems. Theres issues with the M3 SATA being routed via the USB interface internally on the board which causes latency problems and the SATA interface is too slow. I am looking at this again. But might consider possibly getting a W3 board which I think solves this.
Oh, yea. Well at least you know it doesn’t work on M2u either It looks lit is should, but I notice even after making the mods to fstab and uEvn.txt, there is a message at boot time reverting to mounting the filesystem on mmcblk0p2: