SMART status:-- DISK FAILURE IS IMMINENT

Solution 1:

I had this problem which happened to me last year. When it says "Disk failure is IMMINENT", it really means that. Pull whatever data you value off of that, because it won't be long before it fails completely, wiping out what's on it. (Where "Won't be long can range from a day to about a week in my experience")

This is a hardware issue. The disk is physically failing. If it's new enough, check about sending it in under warranty. There isn't any repairing it.

Solution 2:

Apart from contacting your disk's manufacturer, check my answer on What to do if Disk Utility shows bad sectors pending in SMART? as a last solution.

Won't save you the trouble to buy a new drive, or give you piece of mind about your data in this one, but could keep your disk away from the trash can for a while...