Non-Hoster question for the computer experts

[mindonstrike]

A hard drive on my backup computer developed a "bad block" which made the drive non-usable. After several unsucessful attempts at fixing it with chkdsk, chkdsk did finally get it working again and recovered most of the data.

My question is, is a bad block a mechanical failure warrenting replacing the drive or a condition that can be remedied by reformatting or did chkdsk/f fix it good as new (except for the few files it couldn't recover) ?

Thanks for your input.
Sam