slow in opening Finder window

Hi,
I got the new iMac 27" BTO high end machine. First time user of Apple machine. The machine is linked up to 4 external harddisks via usb.

anyway, whenever i open the finder window to view the content of the hard disk. I always have to wait like 10-20 sec or longer.

I suspect that Apple is putting the hard disk to sleep/idle? what is the actual problem and how do i resolve it?

Opening up to view the content of the drive is always slow.

Thank you.
Scott

thanks for the tips.