Hard drive - the most vulnerable spot any server. If you take the possible failure of "iron" that often fails is the hard drive. At the same time there is also a huge risk of data loss (unless of course fails to make backups). Under this state hard drive is required to monitor and replace them immediately after a problem occurs.

This will help S.M.A.R.T., which will constantly monitor the disks and if the problem will notify you by email. S.M.A.R.T. - A technology for self-diagnosis and prediction of possible hard drive failure.