How to check if internal HDD spindle is off after unmount

Question

I use SSD instead of optical drive in my Macbook MC516LL, so I have bunch of reasons why I wants to keep HDD's spindle off:

• Preserve HDD from shock
• Reduce energy consuming
• Reduce overall system temperature

I use diskutil umount HD250 and it disappears from OSx. So how can I check if spindle turned off?

Thanks!