Which S.M.A.R.T parameters are significant?

S.M.A.R.T is Most Important

High speed hard disks, small and crowded chassis can cause very high temperatures. This means that the hard disk is not able to cool down. Disk performance and reliability significantly decrease as temperature increases and above 50 °C failure can occur any time. Disk manufacturers often limit the maximum operating temperature to 50 degree centigrade. However, it is recommended to keep your hard disks at lower temperature (approximately 35-40 °C is good) to increase their life time.

Which S.M.A.R.T parameters are significant?

Not all hard disk support all such S.M.A.R.T. parameters, but here is the list of most significant values:

  • 1 Raw Read Error Rate: Number of hardware read errors occurred when reading from the disk surface. Wrong surface or reading head condition may affect this value.
  • 5 Reallocated Sectors Count: If the hard disk found an error, it tries to reallocate the data to a new, spare location and mark the original sector as reallocated to prevent further usage. This value is the number of such reallocated sectors.
  • 7 Seek Error Rate: Errors found while the head(s) were seeking to a specific sector. This value indicates if there is a head positioning unit (servo) problem.
  • 9 Power On Time: The number of minutes or hours (depends of the manufacturer of the disk) the drive is powered. This value is constantly increasing as “total km” counter in cars.
  • 10 Spin Retry Count: Hard disk could not spin up when the computer is powered and it needed to retry. Increasing this value is a possible sign of a faulty motor.
  • 194 Disk Temperature: The temperature of the disk in °C units. Some models store different values for the disk and the electric board. Some models store not only current but maximum temperature reached also.
  • 196 Reallocation Event Count: Number of reallocation operations started. This indicates both completed or failed reallocation operations.
  • 197 Current Pending Sector Count: Number of “weak” sectors waiting for reallocation. When the reallocation completed, this value may decrease.
  • 198 Uncorrectable Sector Count: Number of uncorrectable errors. This is one of the most important values, it indicates the total number of unusable sectors. Increasing this value means that hard disk failure will be occurred.
  • 200 Write Error Rate: Number of errors found during write operations to the disk surface.

These are the most important values. Some others indicate statistical information but some may be used for prediction of the hard disk status (for example, increasing hard disk spin up time or spin retry count may indicate problems as the hard disk can’t start easily). For the complete list of parameters.