I had a dying drive that smart thought until it totally disappeared was a good drive, and actually all parameters did look fine but this system was causing my system to lockup and other bad behavior:
=== START OF INFORMATION SECTION ===
Device Model: WDC WD20EARS-00MVWB0
Serial Number: WD-WMAZ20139
Firmware Version: 50.0AB50
User Capacity: 2,000,398,934,016 bytes
Device........