Quote from TraderRobb:
Mike:
I use Drive Image with an external hard drive (usb). When the primary drive goes down (never has), you can insert a hew hard drive, boot through a drive image cd when "walks" you through restoring the image from the USB drive to the new hard drive.
The life of hard drives is about 50 human years, using Mean time before Breakdown in engineering terms. This is why I don't see the need to run two hard drives at once in a machine, but larger companies would take such a precautionary measure for sure.