Magnetic Head Assembly Failure

MHA is an abbreviation for ‘Magnetic Head Assembly’.  This can also be referred to as HSA (Head stack assembly)

A magnetic head is approximately the size of a grain of sugar and can be found at the end of an arm that traverses backwards and forwards inside the hard drive chassis to read and write magnetic information to all locations on the rotating disk surfaces.

Modern hard drives have multiple double-sided storage platters.  Each storage surface requires its own dedicated read/write head.

The MHA is a series of heads (one per surface) which move in unison, so that all surfaces can be read or written to simultaneously.

The system is somewhat similar in principle to a vinyl record player, though unlike a record stylus, the magnetic head does not come in contact with the rotating platter surface.   Instead, it ‘floats’ on a film of air generated by the rotation of the platter.

Any disturbance or shock to the disk while rotating can cause the head to momentarily contact the rotating disk surface, resulting in damage to the heads and/or platter.  A power surge to the head pre-amplifier will also render the MHA non-functional.

‘Head-only’ damage is usually a recoverable condition, whereas platter damage usually results in a partially recovery result, at best.

One major problem in the determination of platter damage lies in the fact that in a multi-platter drive, it is generally not possible to fully inspect both sides of each disk platter during the data recovery evaluation process.  Removing the platters individually will cause loss of rotational alignment of the platters as set during manufacture.  Based on a number of other indicators, CDS will confirm cases where it is believed that a MHA replacement is expected to result in a recovery of data.  However, in these cases, there is always a risk that non-visible platter damage may damage the replacement MHA immediately, ultimately resulting in non-recoverability and an invoice for parts consumed, even if no data is recoverable.

Obtaining a Replacement MHA

A replacement MHA is obtained by sourcing an exactly matched ‘donor’ hard drive which is disassembled by CDS to provide the required MHA part.  The ‘patient’ drive is rebuilt with the compatible ‘donor’ components.

Exactly matched drives are sourced from specialist suppliers, usually in the USA or UK. Such companies stock and catalogue refurbished hard drives in a way that they can identify a correct match of critical hard drive attributes such as manufacturer, capacity, firmware revision and other key parameters.

Such specialist sources charge a premium for supply of donor drives, and there is usually a considerable cost element arising from expedited freight using services such as UPS/Fedex/DHL. Standard US post can take up to 4 weeks to reach Ireland!

Multiple Donors

In certain cases, multiple donors may be required so that the failed hard drive can be processed on a staged basis using selective surface-by-surface imaging.  This approach is designed to eliminate the risk of damaging the non-reading surfaces, and involves disabling all but one magnetic head, so that only the associated surface can be read safely in isolation.

Partial Recovery Results

Depending on the nature and extent of damage to the drive, a partial result may be best possible outcome.  Our expert staff will appraise you of the possible outcomes on your hard drive once the evaluation process has been completed.