inside hard disk

Mechanical Failures of Hard Disk Drives

Hard disk drives are fragile devices. The most common reason why CDR receives in hard disk drives with mechanical failures for data recovery is that they have sustained a physical shock. Many of our customers are surprised that dropping their hard disk drive just 2 or 3 inches can lead to a serious failure of the hard disk drive. Given how robust other electronic devices are, like mobile phones and cameras, people have a tendency to consider that their laptop or portable hard disk drive can sustain a similar level of wear and tear. Unfortunately, they can not. Please see our “How do hard disk drives work?” page for further information. Below is a summary of the typical mechanical failures that we see in hard disk drives.

Read / Write Head Failure

On most occasions when there is a failure of the read-write heads the hard disk will spin up and then make a repetitive clicking sound. This is sometimes known as the ‘click of death‘. In general in hard disk drives from 2007 onwards the clicking sound is much quieter, and some models of hard disk drive will spin down after a few seconds if it has failed to initialise.

The read-write heads normally float from between 10 to 100 nanometres away from the surface of the platter during normal operation. If the read-write head were the size of a jumbo jet it would fly 1.5mm off the ground. As you can imagine from this scale any sort of physical shock or contamination in the HDD is likely to affect the normal operation of the heads.

To recover the data when there is a failure of the read-write heads it is necessary to replace the head assembly of the failed hard disk drive with that of a working donor.

Spindle Motor Seizure

The typical symptoms of a motor seizure is for the platters not to spin up, and there will be a quiet buzzing, tapping or beeping noise that will come from the hard disk drive.

In the case of Seagate hard disk drives (particularly the 7200.10 and 7200.11 Barracuda) seizure of the motor bearing is very common after physical shock. So much so that there has been the development of specialist tools just to deal with the motors bearing of these particular series of HDD. In other manufacturers when the motor appears to be seized it frequently does not relate to the bearing, but relates to a phenomenon called “stiction.” Stiction is the static friction that needs to be overcome to enable relative motion. In HDDs the result of two very smooth objects coming into contact (the platter and the head) is that they can become stuck together, preventing the motor from spinning up. It is necessary to use specially designed tools to remove the heads from the surface of the platter to ensure no physical damage is caused to the platter surface, which would lead to data loss. Often the head assembly also has to be replaced as the read-write heads have become damaged.

Occasionally there are seizures of the motor bearings in Samsung and Western Digital hard disk drives. For HDDs made by these manufacturers, it is necessary to perform a platter swap to a donor spindle motor. This is extremely difficult on modern disks and is always the final option in the recovery process.

inside hard disk

(Click to enlarge) A failed HDD with a deep head crash and annotations pointing to key components inside the hard disk drive

Pre-amplifier Failure

The pre-amplifier (or preamp) is a chip which controls the read-write heads and amplifies signals to and from them. The signals generated by the read-write heads are very weak which is why this component is necessary. Preamps cannot withstand static discharges so precautions are required when there is any handing or repair work. Pre-amplifier failures are less common in modern hard disk drives compared with HDD manufactured prior to 2005. Nevertheless, CDR has received a number of 2TB Western Digital HDDs with a preamp failure – it appears there is a particular model which has a high failure rate. Otherwise, the failure of a preamp is typically a result of a bad power surge which has damaged the PCB.

Challenges in Disk Repair

There are numerous challenges regarding the recovery of data from hard disk drives with mechanical failures. The first is correct diagnosis of the fault, followed by finding the necessary correct match donor part. The difficulty in finding donor parts can vary significantly based on the age, manufacturer and model of hard disk drive. CDR keeps a large stock of donor parts for this purpose, but often it is necessary to order donor parts in. We include the cost of these donor parts in any quotation that is given.

The work is delicate and requires specialist equipment. There are instances that data cannot be recovered. This usually relates to physical damage to the platter surface in the form of a head-crash. When the HDD is opened for inspection the top platter surface is examined for physical defects, and the hard disk assembly casting is inspected for contamination which is a typical indicator of a head-crash. If there is evidence of physical damage to the surface of the platter then we shall not continue. Otherwise, the donor parts are used to replace the failed components.

Performing Disk Repair

Working on a hard disk drive with a mechanical failure requires precision tools and a delicate hand. It also requires a suitable clean environment. All work takes place in a class 100 cleanroom or appropriate laminar flow cabinet. In both cases it allows a contamination free environment to work in. Pictured left is a video by HDDSurgery demonstrating a head assembly replacement.

You should not under any circumstances open the hard disk drive to expose the platters. In our experience 7 out 10 HDDs which have been opened prior to arriving to CDR are unrecoverable as a result of mishandling or contamination.

Unfortunately, when we do receive a hard disk drive which has been previously opened it is necessary to charge a non-refundable fee of £60 + VAT. This is the only occasion that CDR makes an upfront fee, otherwise, all of the work that is conducted is on a ‘no-recovery, no-fee’ basis.

Further Information of HDDs

The CDR “How do Hard DIsk Drives Work?” is a good place to start to learn a few of the basic principles regarding the operation of HDDs.

For a detailed and informative explanation of the components which make up a working hard disk drive please see Artem Rubtsov’s 2009 article on HDDScan, titled, “HDD from the inside.”

Further details of hard disk failure can also be found here on Wikipedia.