What do you mean? As an interface, SATAIII is superior to SCSI320 in bandwidth (600MB/s to 320MB/s IIRC), but just because SATAIII has higher bandwidth doesn't mean that a SATAIII drive would necessarily be faster. What model SCSI drive do you have? Maybe there are faster SATAIII drives out there, but without knowing what model you have, I don't even know how fast your drive is.
I am thinking on buying a SAS HHD for it's speed and reliabilty, but I don't what to do a raid! Does anyone have any ideas on hooking it up? I find that the SSD can not be defraged. I bought a 128 Gb SSD for os but it seems when I install a program some of them doesn't give me a oprion to load it on my secondary 3Tb HHD.
defrag is not needed for SSDs, that's why they dont support it. In fact, it's better for an SSD to not be defragmented. SSDs aren't like hard drives which need sequential access to have decent performance because SSDs perform excellently in random access. More than merely detrimental to performance, doing a defrag on an SSD could wear down its flash cells badly.
What programs aren't giving you the option to choose where to install? I'm not aware of any programs that don't let you choose.
For programs that force themselves onto your SSD, you can move the program manually and use a command line command "mklink /d C:\old_path D:\new_path". You have to run the command line as administrator. Any program will continue to work using this method, as it creates a file-system link between the installed path and the actual location of the program (though you should exit the program first). This is also useful if you frequently forget to change the install directory
If you play steam games, get SteamMover.
In my experience though, most applications that auto-install to C are not large enough to matter (like adobe reader/flash).
SSDs don't need to be defragged because they aren't hard disk drives. There is no seek time, therefore they don't benefit from contiguous files, everything is essentially contiguous.
edit: just realized that badcarma is not the OP :\ please don't thread-jack.