OK we have got our hard drive with all it’s parts working properly what else can go wrong?

Well as explained previously the data is contained on the magnetic surface of the drive and this surface can fail. In addition the data written to it can be corrupted and this may occur from power failure
Before we even begin to use a hard drive there are a number of critical areas on the disk which are essential to it’s operation.

The first of these is the system area which contains essential data necessary for the operation of the hard drive. This area of the hard drive must be readable when the drive powers up.

  • Smart Data
  • System Logs
  • Serial Number
  • Model Numbers
  • P-List (Primary Defects List – i.e.: manufacture defect info that does not change)
  • G-List (Grown Defects Lists – sector relocation table)
  • Program Overlays – Firmware, Executable Code, or updates
  • Specific Tables like RRO – (recalibrate repeatable run-out and head offsets)
  • Zone Tables
  • Servo Parameters
  • Test Routines
  • Factory Defaults Tables
  • Recalibration Code Routines
  • Translator Data

When a hard drive powers on it performs a check similar to that which a computer performs when it powers on.

1. The first check is to ensure all of the electronics components on the PCB are functioning.
2. If 1 is successful it then starts the spindle and the drive starts to spin.
3. It then unmounts the heads from it’s PARK rack.
4. Next it will try and read data from the System Area such as Servo Data.

Certain data contained in the System Area is essential for the operation of the hard drive and if this data is corrupt or damaged we can often see strange behaviour.

With Seagate drives this may mean the drive is not recognised or returns an incorrect size. With Western Digital drives a corrupt system area may result in head clicking.

Specialised tools are necessary to access these areas on a hard drive and repair the corrupt areas. It is also possible these areas have become permanently damaged an in this case we may need to perform a hot swap with and identical drive.

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