Can my retina MacBook Pro SSD drive go to sleep? In energy settings there are several options concerning the power consumption of you mac, like dim display, app nap, but also "Put harddisk to sleep when possible".

To my knowledge, an HD hard disk can go to sleep, it will stop spinning and park its heads.

But I have an original SSD build in my retina MacBook Pro. Can this SSD disk go to sleep as well?
As to what I'm aware, an SSD does not classify as a hard disk, therefore it will not go to sleep as part of this option. (I'm not even sure you can make them go to sleep to begin with.)

Using a laptop with an internal SSD as its only form or storage will make this setting of no use. However if there is say an external HDD plugged in, it will abide to this setting.

But back on topic, an SSD will not obey this setting.