Comment 207 for bug 131094

Hendrik: The fact that work on your SATA drive makes the system sluggish, contrary to the PATA one, is normal since your system files are on that drive. Schedulers only deal with processes competing for the same drive access. If the problem is actually with SATA, the only proof we have is that you only changed your drive to SATA, and nothing else.

Anyway, we must be very prudent here since there may be very different issues that affect all users, or only some hardware models. But please go there and report, that can be useful:
http://bugzilla.kernel.org/show_bug.cgi?id=12309