MacBook Pro early 2011 with Seagate sshd gets I/O errors

Hello!

I've mounted a 1TB Seagate SSHD in my son's early 2011 MacBook Pro and unfortunately it does not work quite as expected. We get a lot of I/O errors, sometimes so many that it's not even possible to log in. Here's what we've found out:

1) The 320GB ordinary HD that came with the mac seems to work perfectly

2) The 750 GB ordinary HD that was in the mac before worked fine

3) When mounted in an external enclosure via USB, the 1 TB SSHD seems to work without errors at all (the mac boots fine from the disk and logs no I/O errors)

So there seems there might be a problem with high speed SATA on this machine. I forgot to check the negotiated speed when the 320GB disk was mounted internally, but the speed for the SSHD is 6 Gigabit/s.

So my questions are:

- are there known problems with this mac and high speed SATA?

- if not, what is the most likely problem - cable?

regards,

Espen