Effect of disk support system dynamics on the stability of head–disk interface during an operational shock in a mobile hard disk drive

There has been a substantial increase in the demand of hard disk drives (HDD) for mobile electronic devices like laptop, camcorders, etc. Mobile HDDs are often subjected to harsh working environments and hence require higher shock resistance for better reliability performance. In this paper, we develop a model for the mobile disk drive to numerically investigate the dynamics of the head–disk interface (HDI) during an operational shock. The results show that the disk and its support system design have a strong influence on the shock resistance. This study can help improve the HDD components and air bearing design for a better shock performance.     

HAMR HDD shock responses

Heat assisted magnetic recording (HAMR) and slim mobile hard disk drives (HDD) are being developed parallelly to maintain cost advantage over the solid state drive. Operational shock and non-operational shock capabilities are seriously challenged for the slim HDDs due to reduced stiffness (thickness). It is worse for slim HAMR drives due to additional laser diode (LD) and other necessities being added on slider. Shock tests are part of the key performance matrices that must be passed in HDD reliability tests, and the concerns for HAMR mobile drives are, (1) slider lift-off G-level degradation during op-shock, and (2) LD back-to-back hitting during non-operational shock. We studied a few potential HAMR HGA designs, also analyzed a design that improves drive op-shock performances.     

A study of non-operational dynamic responses of disk in 3.5 in. hard disk drive to impact load

Hard disk drives have to be designed to sustain operational and non-operational shock. There are many analytical models and numerical schemes proposed and many experiments conducted for analyzing the transient impact responses of hard disk drives. The existing researches have been focused on the slider-suspension responses at the head-disk interface in which the linear models have been used and the effects of spindle motor have been ignored. In this study, the complex vibrations of disk of 3.5 in. hard disk drive (HDD) under shock are experimentally investigated. The hammer impact test and linear drop test are conducted for the HDD to study the effect of shock on the disk responses. The results show that the nonlinear rock modes substantially contribute to the vibrations of disk when HDD is under shock impact. The nonlinear properties of the disk responses and the mode damping ratio are evaluated by using empirical mode decomposition approach.     

Thermal analysis of helium-filled enterprise disk drive

Enterprise hard disk drives (HDDs) are widely used in high-end storage systems for data center. One of key performance requirements for enterprise HDDs is data access rate, which demands very high rotational speed (e.g. 15 k rpm or more) to permit fast access time. To reach such high speed, the disk spindle motor draws more power to spin and hence the temperature of HDD enclosure increases due to large windage loss. It has been known, temperature rise is one of the most fundamental factors that affect the reliability of the disk drive. In order to develop high reliable enterprise HDDs, thermal management of enterprise HDDs needs to be optimized to improve heat dissipation. One possible approach is to fill disk drive with helium because of its lower density and higher thermal conductivity. This paper investigates thermal performances of helium-filled enterprise disk drives through FEM simulations with experimental validations. Windage loss and heat convection of the HDD filled with helium and air are analysed. The simulated and measured temperature distributions of one commercial enterprise HDD with helium-filled and helium-air mixture are compared with those of an air-filled one. The results show 41% reduction of temperature rise of HDD enclosure can be achieved by filling with helium in comparison with that of air-filled HDD. It is also projected that in terms of equivalent cooling capability like air-filled HDD at 15 k rpm, helium-filled HDD spindle can spin up to 19 k rpm, which will greatly increase data access rate by 25% for future enterprise applications.     

HybridPlan: a capacity planning technique for projecting storage requirements in hybrid storage systems

Economic forces, driven by the desire to introduce flash into the high-end storage market without changing existing software-base, have resulted in the emergence of solid-state drives (SSDs), flash packaged in HDD form factors and capable of working with device drivers and I/O buses designed for HDDs. Unlike the use of DRAM for caching or buffering, however, certain idiosyncrasies of NAND Flash-based solid-state drives (SSDs) make their integration into hard disk drive (HDD)-based storage systems nontrivial. Flash memory suffers from limits on its reliability, is an order of magnitude more expensive than the magnetic hard disk drives (HDDs), and can sometimes be as slow as the HDD (due to excessive garbage collection (GC) induced by high intensity of random writes). Given the complementary properties of HDDs and SSDs in terms of cost, performance, and lifetime, the current consensus among several storage experts is to view SSDs not as a replacement for HDD, but rather as a complementary device within the high-performance storage hierarchy. Thus, we design and evaluate such a hybrid storage system with HybridPlan that is an improved capacity planning technique to administrators with the overall goal of operating within cost-budgets. HybridPlan is able to find the most cost-effective hybrid storage configuration with different types of SSDs and HDDs     

一种有效的异构盘高能效缓存机制

固态盘具有低功耗、高性能、耐冲击等优势,硬盘具有高容量、低价格等优势.通过改进文件系统的结构,把固态盘和硬盘结合起来,固态盘作为硬盘的大容量缓存,组成一个我们称之为异构盘的异构系统,其性能接近于固态盘,价格却接近于硬盘.同时,在硬盘有足够空闲时长时,使之关闭以减少能耗.针对大容量缓存,我们采用了合适的树形搜索结构,提出...     

Study on flow-induced vibration of head–disk assembly mechanisms in actual hard disk drive

Achieving ultra-high magnetic-recording density in hard disk drives (HDDs) requires clarification of flow-induced vibration issues. In particular, it is necessary to reduce the flow-induced disk vibration called disk flutter. Thus far, however, there has been no experimental research related to disk flutter in actual HDDs. For this study, therefore, the disk-flutter issues have been studied experimentally, using an actual 2.5-in. HDD with one disk and two magnetic heads. The aim was to study the effect of operating magnetic-head mechanisms on flow-induced disk flutter. This study evaluated disk flutter as well as static pressure distribution in the actual HDD, by taking measurements while changing the operating modes of the magnetic-head mechanism as well as the number of operating air-bearing sliders. The study demonstrated that the disk-flutter amplitude increases and its frequency decreases when the magnetic-head mechanisms are operating. It was also found that the amount of decrease in the disk-flutter frequency depends on the number of operating air-bearing sliders whose amplitude increase varies with the specific operating mode of the head mechanisms, such as whether it is in track-following or seek modes. In addition, operation of the magnetic-head mechanisms generated non-uniform static pressure distribution within the HDD. These factors suggest that a decrease in disk-flutter frequency results from the slider-coupled vibration and an increase in disk-flutter amplitude results from the static pressure changes as well as air-following changes, as these vary with the actual operation of the disk head mechanism. From these experimental results, it appears that the disk-flutter issues in actual HDDs should be considered as a system that includes the operation of the magnetic-head mechanisms and disk-coupled vibration.     

Statistical energy analysis on vibrational energy transmission in hard disk drive components

One of the problems found in the 2.5 in. hard disk drives (HDDs) in operation is the vibration of the HDD case. Aiming to find crucial information to reduce the vibration transmitted to the outer shell of HDD, the parameters involving vibrational energy transmission through the main components of HDD are identified by the test-based statistical energy analysis (SEA). First, the vibration tests of HDD in the idle mode are performed in order to identify the contribution of the main components; the top cover, the platters, and the actuator arm to the overall vibration of HDD. The SEA parameters including the dissipation loss factors of the individual components and coupling loss factors of the pairs of the components are then experimentally determined in order to calculate the vibration transmission power among the components. The determined parameters, hence, provide some vibrational energy transmission characteristics to facilitate the design of the HDD components to generate less vibration. With some further studies using this concept, the vibration due to shock exerted to the shell of HDD that is transmitted to main components inside the HDD can also be reduced.     

Human-based evaluation of sound from hard disk drives for noise control

Most recent efforts to reduce the noise produced by hard disk drives (HDDs) have been based on measurable physical quantities such as the sound pressure level. However, given that the purpose of reducing HDD noise is to improve human comfort, it would be better to evaluate noise levels on the basis of human perceptions. To address this issue, we carried out human jury tests on eight HDDs in which people were asked to compare the noise of pairs of HDDs and determine which HDD sounded louder or more annoying. The jury test results were then compared with sound pressure level measurements of the noise produced by the idling HDDs and a discrepancy was found between the human perception of HDD noise and the physical quantities commonly employed for noise control. Psychoacoustic variables such as loudness level showed a better correlation with the jury test results.This research was supported by Samsung Electronics Co., South Korea. The authors gratefully acknowledge the support and encouragement provided by Dr. Young Son and Dr. Yunsik Han.     

Analysis of contact phenomena between a head stack assembly and disk during operational shock

A hard disk drive (HDD) is very sensitive to shock. Increasing portability demands have led to increased HDD exposure to unexpected shocks. Therefore, the dynamic characteristics of an HDD were utilized to investigate the relative behavior of the disk and head stack assembly (HSA) during operational shock. A finite element model of HDD was constructed to simulate operational shock. This model included the spindle system, base, HSA, and disk. The relative behavior of the disk and HSA was analyzed using different bases with different stiffness. A drop test was performed to verify the simulation results. A modified base design was then proposed to protect against contact between the disk and HSA in HDD.     

Design of hydrodynamic bearings for high-speed HDD

 In this paper we discuss the technical issues of hydrodynamic bearings (HDB) for hard disk drives (HDD). We also report results of numerical analysis and of experiments aimed at solving the characteristic problems of high-speed HDDs. Received: 5 July 2001/Accepted: 21 December 2001     

A novel methodology for quantitative evaluation of scratch-induced magnetic damage in perpendicular magnetic recording disks

We proposed a methodology for determining the demagnetization effect (magnetic damage) created by scratches on the surface of the perpendicular magnetic recording disks of a hard disk drives (HDDs). Scratches, which may occur on the disk??s surface during head and disk contact, result in read and write errors on the HDD. Investigating the amount of magnetic damage is thus an important issue. In this study, the scratched area composed of scratches having a fine pitch and shallow depth were generated, and Kerr loop measurements on the normal and scratched area were conducted. Magnetic damage was then estimated from the difference of Kerr loops. By comparing the results of the proposed methodology with the results of a previous methodology using a magnetic force microscopy, it was confirmed that the proposed methodology can be used to quantitatively evaluate scratch-induced magnetic damage.     

A new approach to design safe-supported HDD against random excitation by using optimization of rubbers spatial parameters

Hard disk drives (HDDs) of laptop personal computers (LPCs) are devices vulnerable in harsh mechanical environments. Hence, they need to be protected against damages due to vibration in order to have better read/write performance. In the present study, a LPC and its HDD are modeled as a system with two degrees of freedom and the nonlinear optimization method is employed to perform a passive control through minimizing the root mean square of HDD absolute acceleration due to a base random excitation. The presented random excitation is considered as a stationary, zero mean process with Gaussian distribution. In addition, eleven inequality constraints are defined based on geometrical limitations and allowable intervals of lumped modal parameters. The target of the optimization is to obtain optimum modal parameters of rubber mounts and rubber feet as design variables and subsequently propose new characteristics of rubber mounts and rubber feet to be manufactured for HDD protection against random excitation. In this paper, a nonlinear optimization problem is separately solved for three widely-used cases of HDD by using modified constrained steepest descent algorithm (PLBA) which was extended based on sequential quadratic programming. Finally, the genetic algorithm is used to verify results of the PLBA algorithm.

     

Shock and vibration isolation of laptop hard disk drive using rubber mount

Hard disk drives (HDDs) in laptop personal computers (PCs) are subject to impact-induced failure, as well as to operational vibrations. Elastic mounts with cushioning materials are often used to minimize the likelihood of failure in such cases. In this paper, we analyze the dynamic characteristics and shock response of the vibration isolation systems supporting HDDs. Anti-vibration performance is investigated via position error signal and acceleration transmissibility. Shock response is obtained from a lumped parameter model, based on the nonlinearity of the rubber mounts. Based on the results, we propose guidelines for shock and vibration isolation systems, including a dual rubber mount design.     

Head-positioning control system using thermal actuator in hard disk drives

In this paper, we propose a head-positioning control system with a thermal actuator in hard disk drives (HDDs). The frequency response of the thermal actuator showed that the thermal actuator system has no mechanical resonant mode. Therefore, this head-positioning system with a thermal actuator can control the head-position beyond the major mechanical resonances caused by a voice coil motor (VCM) or suspensions. In this study, the system was a dual-stage actuator system; the first actuator was a VCM, and the second was a thermal actuator. Simulation results for a track-following control in an HDD demonstrated the validity of the proposed method.     

MEMS-based accelerometers use in Hard Disk Drives

 We describe the use of micro electro-mechanical systems (MEMS)-based accelerometers for the compensation of vibrations in commercial hard disk drives (HDDs). Using formal analysis of the HDD mechanics, effects of generic roto-translation on the head position are evaluated. It is shown that such effects can be compensated using feed forward compensation from a weighted sum of the signal provided by two linear and one rotational accelerometer, mounted on the HDD. Rotational acceleration has been obtained using a recently developed MEMS-based, low cost rotational accelerometer. Experimental results presented here show 20 dB disturbance reduction, achieved with a simple, variable gain feed-forward compensator. Received: 5 July 2001/Accepted: 17 October 2001     

PASS: a simple,efficient parallelism-aware solid state drive I/O scheduler

Emerging non-volatile memory technologies, especially flash-based solid state drives （SSDs）, have increasingly been adopted in the storage stack. They provide numerous advantages over traditional mechanically rotating hard disk drives （HDDs） and have a tendency to replace HDDs. Due to the long existence of HDDs as primary building blocks for storage systems, however, much of the system software has been specially designed for HDD and may not be optimal for non-volatile memory media. Therefore, in order to realistically leverage its superior raw performance to the maximum, the existing upper layer software has to be re-evaluated or re-designed. To this end, in this paper, we propose PASS, an optimized I/O scheduler at the Linux block layer to accommodate the changing trend of underlying storage devices toward flash-based SSDs. PASS takes the rich internal parallelism in SSDs into account when dispatching requests to the device driver in order to achieve high performance. Specifically, it parti-tions the logical storage space into fixed-size regions （preferably the component package sizes） as scheduling units. These scheduling units are serviced in a round-robin manner and for every chance that the chosen dispatching unit issues only a batch of either read or write requests to suppress the excessive mutual interference. Additionally, the requests are sorted according to their visiting addresses while waiting in the dispatching queues to exploit high sequential performance of SSD. The experimental results with a variety of workloads have shown that PASS outperforms the four Linux off-the-shelf I/O schedulers by a degree of 3%up to 41%, while at the same time it improves the lifetime significantly, due to reducing the internal write amplification.     

Dimple-flexure contact stiffness effect on operational hard disk drive shock tolerance

A coupled model for simulating the shock response of operational hard disk drives (HDD) is developed. In this model, flexible multi-body dynamics formulation is used to simulate the structure dynamics of the operating HDD while the finite volume method is used to simulate the air bearing dynamics simultaneously. Nonlinearities and discontinuities between the dimple and flexure are considered. Effect of the contact stiffness between the dimple and the flexure on HDD’s shock tolerance is investigated. Results show that the contact stiffness is of critical importance to the shock tolerance of the HDD.     

A more efficient approach for investigation of effect of various HDD components on the shock tolerance

This paper emphasizes the importance of a fast and reliable tool for design parametric studies. Three methods that have been used in studying the shock phenomena in hard disk drives (HDD) are discussed briefly. A more efficient (i.e. faster and reasonably accurate) method is proposed. This new method uses state-space formulation to model the structural components of the HDD and quasi-static concept to model the non-linearity of the air bearing. The structural and the air bearing response, and their coupled interaction are evaluated simultaneously. The computation time and the accuracy of the proposed method are compared against two existing methods: the full finite element model and CML’s HDD dynamics event simulator. The proposed method is found to be much faster with reasonably good accuracy. Experimental shock tests also show that the method is reliable in predicting the shock tolerance of the HDD. A procedure on how to do parametric study with this method is proposed and the effect of overmold and voice coil stiffness on the shock tolerance is studied.     

Tuning of a digital disk drive servo controller using fixed-structure H ∞ controller optimization

 To address the problem of improving the positioning accuracy of the read write head of hard disk drives (HDDs), we present a tuning methodology for the HDD servo controller based on the fixed-structure H _∞ controller optimization. Since optimization is carried out under the fixed controller structure without any additional sensor, no extra cost is introduced. The effectiveness of the proposed method is demonstrated by simulation and experimentation. Received: 13 September 2001/Accepted: 20 February 2002