sakamoto@SakamotoServer:~$ sudo smartctl -x /dev/sdc
smartctl 5.41 2011-06-09 r3365 [x86_64-linux-3.8.0-29-generic] (local build)
Copyright (C) 2002-11 by Bruce Allen, http://smartmontools.sourceforge.net


Probable ATA device behind a SAT layer
Try an additional '-d ata' or '-d sat' argument.