Difference btwn HDD R/w and HDD Scan

I am trying to figure out if there is a problem with my Hard Drive. I am have a difficult time trasnfering my song to my ipod. My playlists will transfer, but there is absolutely no music on my ipod anywhere.

I am in the diagnostic mode and am wondering what the difference is between HDD R/W and the HDD Scan. Anybody know?