Difficult donor parts – HDD headmap mismatch

Hard to find donor parts for HDD recovery.

This is a hard disk drive that we received earlier in the month. The HDD had a failure of the read/write heads. The owner provided what looked to be an excellent match donor hard disk drive. It was purchased at the same time as the failed HDD. All of the critical parameters matched on the front label of the HDD. A full match on the model, firmware, DCM code and even the date of manufacture. Ideal, one would think.

Then we opened up the hard disk drive (see below). Can you spot the difference?

WD My Passport headmap

Two ‘identical’ Western Digital My Passport hard disk drives. Not only did these have different head maps, but a different number of active surfaces.


We were left agog to find the donor HDD with a single platter with a 2 head configuration, and the patient HDD with a two platter 3 head configuration. The ‘headmap’ of the hard disk drive is critical to data recovery process. The headmap tells us the number and order of the active platter surfaces.

Why might this be? During the manufacturer test process if a platter surface does pass the requisite benchmarks for quality it will not be used. To ensure there is not waste, rather than throw out the entire platter the surface is simply not used and a read/write head is not assigned to that surface. As you might expect this is a cost-saving exercise that the manufacturers employ.

Finding just the right donor part is an extremely important aspect of the data recovery process. Donor parts from specialist hard disk dealers are typically priced 2-3 times higher than a disk purchased from your local IT supplier. A specialist HDD will provide all of the parameters listed on the front of the HDD, however they usually cannot tell us the headmap associated with the disk. This is only possible by visually inspecting the hard disk assembly (not recommended), or using a device like the PC3000 to determine the head map electronically.

We have found that this variability in HDDs has increased in recent years and it is becoming more difficult to find a donor parts based only on the parameters listed on the front of the hard disk drive. There is always a chance that what we purchase in to attempt the recovery will not be an appropriate match. This can mean ordering multiple donor parts for each job. This is just one of the significant costs associated with data recovery. In these cases we still hold a fixed price quotation, regardless of how many donor parts are ordered to attempt the work.