What is a head crash?
A head crash is a failure of the read/write head in a hard disk drive. It occurs when the head makes physical contact with the disk platter surface, often due to a shock, vibration, or manufacturing defect. This contact can damage the thin magnetic coating on the platter as well as the head itself.
What causes a head crash?
There are several potential causes of a head crash:
– Shock/vibration – If a hard drive receives a significant shock or vibration while operating, the head can smash into the platter. Dropping a laptop is a common cause.
– Contamination – Dust particles inside the drive can cause the head to stick and hit the platter. Smoke particles can also condense on the platters.
– Wear and tear – Over time, the suspension holding the heads can weaken and allow uncontrolled movement. The platters can also develop bumps or pits.
– Manufacturing defects – Improper assembly, faulty components, or bad firmware can all lead to crashes during normal operation.
– Overheating – Excessive drive heat expands components and throws off the precise head positioning, potentially bringing it into contact with the platters.
What are the parts of a hard disk drive head?
The read/write head is composed of several delicate parts:
– The slider – The block that rides just above the disk surface on a cushion of air. It is designed to maintain a consistent small gap between the head and platter.
– The suspension – The arm that holds the slider and allows it to move across the radius of the disk. It provides controlled flexing to keep the slider at the right height.
– The coil – Writes data by converting electrical signals to magnetic fields. It is located on the trailing edge of the slider.
– The magnetoresistive element – Reads data by detecting small magnetic field changes in the platters. It is located at the leading edge of the slider.
– The head flex cable – The wiring that connects the head to the drive’s circuitry.
What happens during a head crash?
When a head crash occurs, the head slamming into the platter can cause both physical and magnetic damage. Here’s an overview of the sequence:
1. The head loses proper clearance from the platter surface, either through shock or a malfunction.
2. As the head gets closer to the rapidly spinning platter, air friction heats up the slider.
3. The head makes contact with the platter, often at speeds of over 100 mph. This instantly shatters the fragile slider.
4. The exposed electrical elements of the head short out against the platter surface, damaging the coil and sensors.
5. The force of the impact scrapes a radial groove into the magnetic material coating on the platter. This can destroy stored data.
6. Bits of the disintegrated slider can gouge out pieces of the aluminum substrate beneath the coating as well. These leave concentric scratch rings on the platter.
7. Secondary collisions can occur if platter damage leads to increased vibration. Shock waves can also displace internal drive components.
What does the damage look like?
Visually inspecting the platters and heads after a crash can reveal distinct patterns of mechanical and magnetic damage:
– A visible radial scrape mark cuts across the platter surface, usually originating from the outside diameter. This scrape exposes the aluminum beneath.
– Within the primary scrape, the coating is often shredded, with flag-like flakes bent in the direction of disk rotation.
– Microscopic examination shows the aluminum substrate gouged with deep, ring-shaped scratches along the scrape path.
– The original scrape mark fractures off into hairline radial cracks extending across the platter. These develop as stress radiates outward.
– On the head, the slider has broken away completely, leaving exposed electrical components dangling from the suspension.
– Insulation burns, melted coils, and electrical arcing can occur on head elements making direct contact with the platter.
– Magnetic force microscopy reveals erased and corrupted data bits trailing in arc shapes behind the scrape mark.
Can a head crash lead to complete data loss?
Head crashes often result in severe data loss, but the extent depends on the nature of the damage:
– A minor scrape that only damages a small section of one platter may allow much of the drive’s data to be recovered.
– A strong impact that knocks heads into multiple platters is more likely to cause complete data loss.
– Data concentrated along the scrape path is usually not recoverable, while information elsewhere on the platters has a better chance.
– Drives with higher aerial density platters are more vulnerable to data loss from fine scratches.
– Data likely cannot be recovered if the heads or drive circuitry are badly damaged. The platters may need to be placed in an identical working drive.
– Quick powering off the drive after a crash can help prevent further secondary damage. But data in buffers and caches may be lost.
So while total data destruction is possible, experienced recovery experts using specialized tools can often retrieve at least some data depending on the drive model and type of head crash damage.
What does a healthy hard drive look like internally?
When everything is working properly, the inside of a hard disk drive looks dramatically different than after a crash. Here are the key characteristics:
Platters
– Shiny and reflective metal surfaces, usually an aluminum alloy or glass material.
– Thin uniform coating of magnetic material across the entire platter, typically 10-20 nanometers thick.
– No visible scratches, gouges, or other blemishes on the substrate or coating.
Head Stack Assembly
– Heads are completely intact, with the delicate sliders and suspensions clearly visible.
– No signs of mechanical wear like cracks or metal flakes.
– Clean electrical connections from heads to preamplifier.
Drive Internals
– Minimal particulate contamination. No stray metal shards or large dust buildup.
– All components neatly in place. Screws and connectors fully secured.
– PCBs (printed circuit boards) intact with no burned spots or damaged traces.
– Motor spindle rotates smoothly and quietly with no wobble.
– No rattling or loose objects that could vibrate and touch the platters.
Operational Performance
– Quiet operation with no grinding or excessive noise.
– No recurring clicking or beeping noises pointing to mechanical malfunction.
– Read/write heads accurately following tracks with no delay.
– No detected problems with reading data, ECC errors, or dropped commands.
– Benchmark testing shows expected performance for the drive model.
When all these conditions are met, you can be reasonably confident that the drive internals are in good working order with platters and heads undamaged.
How can you try to recover data after a head crash?
If valuable data is still needed from the drive after a head crash, recovery should be attempted only by a professional service. But here are some basic steps they may follow:
Evaluate the damage
– Open the drive in a cleanroom environment to avoid contamination.
– Check if the heads and platters are still partially intact and removable.
– Assess which components can be salvaged or require replacement.
Replace damaged parts
– Swap out broken head assemblies with matched spares if available.
– Repair or replace any damaged internal drive components like the motor.
– Perform realignment procedures using specialized tools.
Image the platters
– Spin up platters in a drive or platter imager designed to tolerate defects.
– Create sector-by-sector images of the platter surfaces while error ignoring damaged areas.
Rebuild data
– Remap corrupted regions of the disk image offline.
– Apply advanced recovery techniques like interpolating between good sectors.
– Utilize file carving to extract data without relying on file systems.
Cleanroom transplant
– If drive is totally non-functional, move platters to an identical working drive.
– Replace drive circuit board if necessary.
– Image platters in the surrogate drive.
This is a general overview only – actual recovery procedures require significant expertise. The chances of recovering data depend heavily on the severity and type of head crash.
Can you prevent a head crash through early detection?
Catching the signs of a head crash before it occurs can help avoid complete failure in some cases. Here are warning signs to watch for:
Unusual noises
– Grinding, scraping noises from the drive heads. Indicates they are making contact.
– Beeping alarms. Electronics may detect mechanical problems.
– Clicking noises from the head actuator. Could mean imminent failure.
Performance issues
– Higher than normal disk errors reported by SMART monitoring.
– Bad sectors detected during scanning. Failed reads and writes.
– Difficulty writing to certain disk regions, or loss of previously readable data.
Physical signs
– Increased vibration and temperature from the drive.
– Visible flakes or specks around the drive exterior. Particles may be escaping.
– Strange odors from overheating components.
Preventative steps
If unusual symptoms appear, quick action can help:
– Immediately stop disk access to prevent further damage.
– Copy critical data to another drive as soon as possible.
– Check for external causes like faulty equipment or excess vibration.
– Run manufacturer drive diagnostics and self-tests.
– Consider replacing the drive if internal damage is confirmed.
While not always possible, catching damage early greatly improves the chances of data recovery and avoiding a catastrophic head crash through a controlled drive retirement.
Conclusion
A head crash results in both physical and magnetic damage that can be visually identified on the platters and heads after opening a failed hard drive. The degree of damage determines the likelihood that any data can be recovered – often only a professional data recovery service has a chance. Careful monitoring for symptoms can sometimes detect early signs of head crash and allow data to be saved before complete failure. Handle drives gently, minimize vibration, and pay attention for any unusual behavior to help prevent these catastrophic events.