Shock Protection System
A Quantum White Paper
Most of us give little thought to the hard disk drive inside our PCs, even though it is the most critical part of the system. One can easily replace a monitor, processor, memory, power supply, CD-ROM or floppy drive with only minor inconvenience. The loss of a hard drive, however, could entail the loss of years of data: company records, tax information, school projects, digital family photo collections, etc. Given the steady improvements in product reliability, the risk of data loss today is low.
Drives can fail for a variety of reasons, but here we will address the effect of shock on the drive, and in particular, the potential for protecting long term reliability. At Quantum, our obsession with quality has led us to develop a system that will help protect the drive after it leaves our closely controlled manufacturing environment and is removed from the packaging.
This paper describes the causes and effects of some handling problems for hard disk drives that typically occur before the drive is installed in a system. Quantum’s Shock Protection System (SPS) prevents those events from having a detrimental effect on a drive’s long term reliability and data integrity.
Shock levels are expressed in terms of acceleration and are measured in multiples of the acceleration due to gravity or Gs. The duration of the shock is also important, for it is the combination of shock level and shock duration that determine the effect on the drive.
Hard disk drives are amazingly complex, high precision, electro-mechanical devices. They are very sensitive to external shock and vibration. For example, dropping the drive onto a bench can damage the drive internally with no exterior evidence of damage. The first indication that there is a problem is when the drive does not work after the PC is first switched on for test at the factory. Even worse, the drive can suffer internal damage, which does not lead to immediate failure, but can lead to deterioration over time so that data integrity is threatened.
Quantum and other drive manufacturers spend a good deal of effort educating people on how to handle drives. PC system manufacturers and distributors go to great lengths to train their assembly personnel to ensure that they understand how to avoid damage. While the likelihood for damage is reduced, employee turnover and the move towards channel assembly and local configuration can present challenges for the system manufacturer in maintaining close control over the assembly process.
The drive is most vulnerable when it is removed from the original packaging, which is carefully designed to protect the drives after they leave the closely controlled manufacturing environment. Once the drive is assembled into the PC, it is relatively safe from external damage. The PC casing typically dissipates the energy so that the shock level experienced by the drive is very low.
It is not surprising that the drive can be damaged when dropped onto a hard surface. But a comparably high level of shock can be induced by tapping the drive with a hand tool such as a screwdriver, by clicking two drives together, or by forcing a drive into its location. Figure 1 shows the relative effect of different types of shock events on a drive.
The most damaging events are those with a high shock level and short duration, typically hundreds of Gs with a duration of less than one millisecond. These short, sharp shocks are outside the normal specification for hard disk drives, but can easily occur if little attention is given to handling procedures.
The most common type of damage when a drive is dropped or shocked is called a "head slap." A head slap occurs when sufficient shock is applied to a drive so that the head lifts up off the disk, is whipped back down and bounces around on the surface of the disk. The result is that the head digs into the surface of the disk creating surface damage, and tiny particles or debris can be scattered, as shown in Figure 2. This all happens on a microscopic level, but the high precision nature of a hard drive means that the drive could fail at a later stage if some of the debris lands on a data zone or if the debris becomes wedged between the head and the disk.
Special Considerations for MR Heads
Thermal asperities are a common phenomenon in magnetoresistive (MR) heads and giant magnetoresistive (GMR) heads. The read element in these heads is made of a very thin film of material. This material has the special property of changing its resistance to electrical current in the presence of a magnetic field. As the head flies over the magnetic domains on the disk, which represent the stored information, changes in the resistance of the read element are detected by the read channel.
If the head contacts a small piece of contamination or a surface imperfection, the read element instantaneously heats up. This heat change causes a massive change in the resistance of the film and the signal from the head is so distorted that the read channel is unable to distinguish the magnetic domains - and unable to retrieve your data.
Debris scattered by a head slap event could generate thermal asperities well after the event, and could ultimately lead to the failure of the drive.
One possible solution would be to ensure that everyone who touches a hard disk drive, handles it in a way that would prevent the drive from being damaged. This is very difficult to achieve, because 30 percent of all hard disk drives are not installed by the original system manufacturers’ trained personnel. Many incidents are the result of accidents, as opposed to carelessness.
Another solution would be to design permanent protection around the drive. This potential solution is more costly and would take the drive out of the accepted form factor.
The best solution is to design the drive such that the specific types of handling events can be endured by the drive with no damage occurring. This is the approach adopted by Quantum Corporation in developing a cost-effective way to improve the robustness of the drive, and enhance long term reliability.
The Shock Protection System
New methods of analysis have brought better understanding of the interaction between all the components in the drive. It is only by considering the drive as a complete mechanical system that the effects of shock events can be fully investigated. The information gained can be used to modify and tune different components so that shock events can be absorbed through the drive, preventing damage to the sensitive elements inside.
By carefully analyzing the results of this type of investigation, Quantum has developed the Shock Protection System™ (SPS). SPS minimizes failures arising from head slaps by virtually eliminating head slap as a failure mechanism. Again, damage is caused when the head is allowed to lift off the disk and whip back down onto the disk. Quantum's approach to this problem is to avoid the damage to the disk by minimizing the head from lifting, as shown in Figure 3. The shock is dissipated through the rest of the drive. This prevents head slap, and no debris is created to propagate future failures.
The SPS™ is Quantum’s latest demonstration of technology leadership that provides direct benefits to buyers of data storage products. The SPS™ delivers several benefits: fewer returns for damaged drives, greater data integrity and a more robust hard drive.
Some failure mechanisms that can result from shock take time to manifest themselves. Using a drive that is resistant to those short sharp shocks increases the degree of confidence in the long term reliability of your drive and your data. We may not be able to ensure that everyone handling drives never slips with a hand tool or knocks two drives together, but Quantum’s Shock Protection System™ ensures that your drive has the best protection possible.