Why do hard drive heads fail?

Hard drive heads are a crucial component of computer hard drives. They are responsible for reading and writing data on the drive’s spinning platters. Over time, hard drive heads can fail due to a variety of factors, leading to potential data loss and drive failure. Understanding why drive heads fail can help predict problems and take steps to prevent failure.

What are hard drive heads?

Hard drive heads are small electromagnetic devices that read and write data on a hard disk drive’s spinning platters. The platters are made of a magnetically sensitive material and spin at very high speeds, typically 5400 or 7200 RPM.

There are usually multiple platters stacked on top of each other within the hard drive. Each platter has two heads, one for each side. The heads float nanometers above the platter surface on an air bearing created by the spinning disk. They move in and out across the radius of the platter to access different tracks.

Data is written by applying a magnetic charge to the platter surface with the head. It is read back by detecting changes in the magnetic fields with the head as it passes over. Hard drive heads are incredibly precise devices – a modern drive head may have a gap of just a few nanometers wide at the tip!

How do hard drive heads fail?

There are several mechanisms that can cause hard drive heads to fail over time:

Wear and tear

Like any mechanical component, drive heads experience wear and tear over many hours of usage. The heads are subjected to friction from air resistance at their high velocities. They also make physical contact with the platter surface at startup and shutdown. This can gradually erode the head over time.


Dust particles or smoke residue inside the hard drive can stick to the heads and platters. This contamination buildup can interfere with the heads ability to read and write. It may cause them to crash into the platters.

Thermal stress

Heads are subjected to thermal expansion and contraction as drive temperatures fluctuate during use. This stressed the components and joints. Thermal cycling over years of use can fatigue the materials.

Shocks and vibration

Being dropped or subjected to excessive vibration can knock drive heads out of alignment. This makes them unable to read some tracks. Severe shocks can cause the heads to strike the platters.

Electrostatic discharge

Build up of static electricity from improper handling can discharge through the heads, damaging the sensitive electronics.

Motor failure

If the spindle motor fails, the platters can stop spinning while heads are still positioned over them. This causes the heads to crash into the platters below.

Head crashes

A head crash or platter strike is when the head makes forceful contact with the platter surface. This can chip the platter coating and damage the head. Debris from even a minor crash can also get caught in the head gap, interfering with reads and writes.

What are the consequences of head failure?

Failed heads can lead to the following problems:

  • Inability to read or write data – with damaged heads, some or all data becomes inaccessible.
  • Crashed drive – severe head failure can make entire drive stop working.
  • Data loss – Shock damage to heads can destroy data stored on platters.
  • Corrupted data – Debris stuck in heads leads to bad reads and writes.
  • Performance drops – Worn heads work poorly, reducing data transfer speeds.
  • Error messages – Damaged components trigger S.M.A.R.T. errors from the drive.
  • Noisy operation – mechanical problems create audible clicking or scraping.

At first, only some sectors may be affected by failing heads. But over time, the problem can spread until the drive completely fails. Any important data should be immediately backed up at the first signs of trouble.

How can hard drive heads be protected?

Some steps to help prevent head failures include:

  • Handle drives gently – avoid physical shocks and impacts.
  • Control drive temperature – keep within operating range.
  • Use surge protectors – prevent power spikes.
  • Ground yourself when handling – prevent ESD damage.
  • Filter dusty air – keep drive internals clean.
  • Ensure proper drive parking – platters stop before power off.
  • Replace older drives – newer models have better reliability.
  • Check S.M.A.R.T. stats – monitor for early warning signs.

Enterprise and NAS drives designed for constant operation tend to have the most robust heads. Consumer-grade drives are less tolerant of long term wear and tear.

How are drive heads constructed and attached?

Engineers work diligently to optimize hard drive heads for reliability and precision. Here are some key design elements:

  • Head slider: Aerodynamically shaped ceramic platform that the head components are mounted to. Provides the air bearing.
  • Read/Write elements: Tiny copper coils for writing flux lines. Magneto-resistive sensors read the magnetic fields.
  • Flexure: Thin metal piece that attaches the slider to the suspension. Allows some motion.
  • Suspension: The load beam arm that holds the head out over the platter.
  • Actuator: Moves heads in unison over the platters for seeking.
  • Bearings: Allow actuator rotation.Made of smooth stainless steel.
  • Voice coil motor: Electromagnet coils that finely position the actuator.

The head fly height is so small that a fingerprint on a drive platter could crash the heads into it. State of the art manufacturing is needed to construct such intricate mechanical and electronic components.

How are heads positioned and calibrated?

The track following servo system controls the positioning of hard drive heads with extreme accuracy. Here is how it works:

  1. Servo patterns are written to reserved servo sectors on the platter surfaces.
  2. As each head passes over the servo tracks, it reads burst patterns.
  3. The signal patterns let the drive know if the head is on track or not.
  4. A closed feedback loop makes continuous adjustments to keep heads centered.
  5. Microactuators on some drives provide finer tuning.

Modern HDDs have very narrow track widths, down to just a few micrometers. Even slight head misalignments lead to read/write errors. The servo systems keep everything aligned despite vibration, shocks, and temperature changes.

How have heads evolved over time?

Engineers have innovated and improved hard drive heads over many product generations:

  • Earlier ferrite heads were large and fragile.
  • Thin-film inductive heads increased storage density.
  • MR and GMR elements enabled higher sensitivity.
  • PMR writing handles narrower tracks.
  • TMR heads push aerial density limits.
  • New materials withstand higher temperatures.
  • Nano-scale components boost precision.
  • Heads have shrunk enormously – from the size of a sugar cube on 1950s drives down to just nanometers today!

Advances in drive heads have been key to the phenomenal growth in hard disk capacity over the decades while costs have dropped. But tiny, precise modern heads are more vulnerable to damage. Improved designs try to strike a balance between density gains and reliability.

How do S.M.A.R.T. errors indicate head problems?

Self-Monitoring, Analysis and Reporting Technology (S.M.A.R.T.) provides metrics from the HDD to monitor conditions and predict failures. Two important S.M.A.R.T. indicators of head issues are:

Reallocated sectors count

This shows the number of bad sectors that have been replaced with spares due to read/write failures. A rise in this value indicates problems reading data due to head damage or misalignment.

Reported uncorrectable errors

IO device errors that could not be recovered from. Indicates serious problems with writing or reading data due to heads not functioning.

A drive should be replaced immediately if either of these raw values are rapidly incrementing. The overall “Drive health” S.M.A.R.T. status will change from OK to Warning or Failure once thresholds are exceeded.

What techniques are used to manufacture heads?

Making hard drive heads involves advanced manufacturing techniques, including:

  • Photolithography – Using light to pattern microscopic circuits and components onto the head materials.
  • Thin film deposition – Layering metals, ceramics and magnetic films to nanoscale thicknesses to build up head structures.
  • Ion beam milling – Precisely cutting and shaping head contours using focused ion beams.
  • Wafer dicing – Cutting microscopic sliders out of ceramic wafers.
  • Resistive and inductive coils – Adding read sensors and microscopic write coils.
  • Nanoimprinting – Using molds to pattern nanoscale features on head surfaces.

Clean room assembly is required to prevent microscopic dust from interfering with such small parts. Quality control testing ensures heads meet stringent error rate standards before installation in a drive.

How are heads positioned so close to platters?

Maintaining minuscule clearance between heads and high speed platters is an ongoing balancing act. Several design elements help:

  • The flexible head suspension and gimbal allows the slider to pitch and roll slightly to adjust its angle and keep the air gap constant.
  • Small thermal actuators on the suspension provide nanometer adjustments.
  • External air pressure inside the hard drive counteracts atmospheric pressure to prevent heads from being pushed down.
  • Aerodynamic head surface design enables air bearings at very low heights.
  • Head loading ramps outside the platters lift the heads during spin up and down.

Heads initially “fly” 50 to 100 nanometers above platters during operation. Improvements in fly height control allow modern drives to operate with less than 10 nanometers of clearance!

How are read/write elements constructed?

The reader and writer components packed into tiny head structures represent leading edge nanotechnology. Some key elements include:

  • Reader shields – Permalloy layers that channel magnetic flux to sensor.
  • Seed layer – Starts crystal growth for precise sensor films.
  • Free layer – Magnetic thin film storage layer.
  • Tunnel barrier – Insulating layer just a few atoms thick.
  • Pinned layer – Reference magnet with fixed orientation.
  • Cap layers – Protect outside of sensor stack.
  • Writer coils – Microscopic copper electromagnets.
  • Write poles – Magnetic flux lines channeled across tiny gap.

Elaborate structures and exotic materials like gallium arsenide are used. Each layer must be flawlessly formed on an atomic scale, no thicker than a few nanometers.

What governs the lifespan of heads?

Several factors determine the functional lifespan of hard disk heads before failure:

  • Total operating hours – More uptime equals more cumulative wear.
  • Start/stop cycles – Wear from contact during spin up and parking.
  • Distance traveled – Total area of platter surfaces traversed.
  • Operative environment – Temperature, shock, vibration, contaminants.
  • Workload – High I/O and dense data patterns accelerate wear.
  • Design and materials – Later generation heads are more robust.
  • Maintenance – Preventing damage through proper care and handling.

On average, drive heads may last between 3 to 5 years with moderate to heavy use. Mission critical enterprise drives are rated for much longer – over 2 million hours MTBF. But real-world longevity can vary significantly.

How are heads electrically connected inside the drive?

Flexible interconnect cables relay signals to and from the rapidly moving heads. Key connections include:

  • Preamp – Initial signal amplification near the heads.
  • Arm electronics – Circuits mounted on the actuator assembly.
  • Internal flex cable – Runs along the actuator arm to control head motion.
  • External flex cable – Connects arm electronics to the drive controller board.
  • Plated gold traces – Prevent corrosion of connections.

Thin printed cables only 0.025 mm thick are carefully routed to enable full actuator motion. Their small size keeps mass low to reduce head positioning forces.

How are heads protected when not in use?

Drives use retract systems to safely park the heads when not active:

  • Landing zones – Specify platter areas for parking heads.
  • Ramps – Load/unload ramps outside the platters lift all heads together.
  • Latch – Magnets or mechanical locks fix actuator in parked position.

Removing heads from proximity of platters prevents damage from shocks. Parking routines are crucial to avoid potential data loss.

How are head failures diagnosed?

Some best practices for identifying faulty heads:

  • Monitor S.M.A.R.T. attributes – Especially reallocated sectors and read errors.
  • Scan drives with manufacturer tools – Identify bad sectors physically.
  • Check drive error logs – Commands like ‘dmesg’ on Linux.
  • Listen for odd noises – Scraping or loud clicks signal issues.
  • Benchmark speed – Drops may indicate problems.
  • Stress test with I/O – Heavy workloads trigger failures.
  • Compare multiple drives – Localize problems to individual units.

Troubleshooting and ruling out other components like controllers helps isolate head faults. But often, heads display no obvious symptoms before suddenly failing catastrophically.


Hard drive heads are complex electro-mechanical components tasked with the crucial role of reading and writing data on spinning platters. Their precision and robust operation are critical to overall drive reliability. However, many factors from wear to manufacturing defects can degrade heads over time leading to failure.

Understanding the principles of how heads work and how they can fail assists in prevention and early detection of problems. Careful handling and monitoring of drives allows catching issues before they result in data loss. But inevitably, heads have a limited service lifetime and must be replaced when they start to fail.

Continued engineering of head materials, designs and production methods aims to strike a balance between the relentless pressure to increase aerial density while maintaining acceptable longevity. Expect further incremental improvements as HDD technology persists into the future despite competition from solid state storage.