Depends on whether you actually have a second drive or not? More likely, its a secondary partition on a single drive as mentioned? Some users replace their notebook DVD drive with a second HD or SSD drive.
If you have a single HD, and your diagnostic software is indicating an eminent HD failure, than you need to act quickly if your image backup is on your secondary partition. Restore from your image backup to a new hard drive, using an external USB drive adapter, without delay. You'll also need an image restore USB or CD/DVD boot disc you either previously made or supplied by the notebook maker.