Impact Of Sound On Computer Hard Disk Drives And Risk-Books Pdf

Impact of Sound on Computer Hard Disk Drives and Risk
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IMPACT OF SOUND ON COMPUTER HARD DISK DRIVES AND RISK MITIGATION MEASURES. Introduction to Data Center Acoustic Sensitivity, Data centers are relied upon to store and distribute valuable information from customers across many industries. from the investment banking to the healthcare sector This valuable information is primarily stored on Hard Disk. Drives HDD Industry demands that data centers remain functional 24 hours a day 7 days a week 365 days a year. Downtime can damage the reputation of a data center and result in the loss of customers The data center market. aims to continuously reduce the risk of downtime or lost operation time. One method to help reduce that risk is to install inert gas fire suppression systems Data center fire suppression. system discharges Rawson Green 2007 along with independent testing Nickerson Green Pai 2013. have shown that HDD performance may be reduced or permanent HDD damage may occur due to exposure to. high acoustic levels In order to gain a greater understanding of the impact of acoustic energy on hard drives. Tyco Fire Protection Products now Johnson Controls in conjunction with Michigan Technological University. MTU conducted a holistic study of HDD performance with respect to acoustic energy room acoustics. and suppression system nozzle acoustics This paper incorporates the results of that study and covers the. following topics, Analysis of Hard Disk Drive Acoustic Performance Characterization of noise induced performance degradation. of a sample set of HDDs typically installed in data centers. Understanding Sound Measurements Introduction to the acoustic source path receiver model and proper sound. measurement metrics, Suppression System Discharge Acoustics An overview of the sound generated during fire suppression discharge. events Analysis of nozzle technology specifically designed to lower the sound pressure within the protected area. which reduces the acoustic induced damage to hard disk drives. Acoustic Calculator A method to estimate the sound pressure level within a protected data center. Additional Risk Mitigation Actions Identification of additional actions that can help to reduce sound pressure. levels in data centers,ANALYSIS OF HARD DISK DRIVE ACOUSTIC PERFORMANCE. Hard Disk Drives are storing the information of the connected world HDD technology continues to evolve in terms of. storage capacity and access speeds Over the past few years evidence has been building that suggest HDDs have become. more sensitive to noise as the technology evolves In order to quantify the acoustic sensitivity of current HDDs Johnson. Controls initiated a joint research project with the Dynamic Systems Laboratory at Michigan Technological University. Together Johnson Controls and MTU developed a robust scientific approach to analyze and quantitatively document. the acoustic sensitivity of HDDs, A sample of 12 enterprise model HDDs were selected to represent the population of HDDs that are commonly.
found in today s data centers The 12 HDDs contained samples from five different brands with capacities ranging. from 320 gigabytes to 10 terabytes, The MTU Dynamic Systems Laboratory established an experimental test set up designed to quantify the read write. performance reduction of HDDs when exposed to noise across frequency bands and at varying sound pressure. levels The test setup employed a data acquisition system to control the testing process record the sound pressure. levels SPL in one third octave OTO bands and evaluate the HDD read write speeds. IMPACT OF SOUND ON COMPUTER HARD DISK DRIVES AND RISK MITIGATION MEASURES. The HDDs were placed in an anechoic chamber sound proof chamber to avoid unwanted path effects such as. reflections or spurious external noise sources The testing setup ensured precise control of the noise SPL at the. surface of the HDD by utilizing a real time control system capable of dynamically adjusting the input signal to the. noise source, This SPL control was achieved by means of a feedback loop in the data acquisition system The feedback control. system consisted of a power amplifier compression drivers an electrical current probe and a surface mount. microphone located on the top surface of the HDD The data acquisition system used the real time SPL reading. at the HDD to adjust the noise output of the compression drivers and ensure a constant noise application during. each test The unweighted SPLs were measured in one third octave OTO bands The block diagram of the test. measurement and feedback control system is shown in Figure 1 Figure 2 shows photographs of the experimental. test set up, Figure 1 Block diagram of the test set up The HDDs were placed in an anechoic chamber and were exposed to. sound produced through the speakers by the signal generator. Figure 2 Photograph of the test set up showing the HDD on an MDF board in the anechoic chamber at Michigan. Technological University with the speakers placed 0 5 m above the HDD left The surface mount microphone a fan. used for cooling the HDD and the USB 3 0 cables used for performance test right. IMPACT OF SOUND ON COMPUTER HARD DISK DRIVES AND RISK MITIGATION MEASURES. The HDD performance during the acoustic testing was captured by monitoring the drive read write speeds. The read write performance was conducted using a random process of different sized data packets The block. sizes of the data packets varied from 10 KB to 8 MB The write test was performed first followed by the read. test for all experiments Baseline read write speed tests with no sound source present was captured for each. HDD to establish the normalized 100 drive performance level Once the baseline was established the HDDs. were then subjected to the acoustic sensitivity testing Several baseline tests were conducted throughout the. evaluation of each HDD to ensure no permanent damage had been induced by the testing Each of the HDDs. were exposed to noise in OTO bands from 500 Hz to 10 kHz for sound pressure levels at the HDD surface. ranging from 80 dB to 130 dB re 20 Pa The noise was increased in 5 dB increments until the drive read. write speed performance was reduced by 50 from the baseline The threshold of acceptable performance was. defined as a 50 reduction in the baseline HDD read write performance This limit was established because HDD. performance was noticed to rapidly decline at sound pressure levels above the 50 performance reduction point. Figure 3 shows an example of the rapid reduction in performance at SPLs above the 50 performance curve. During individual HDD testing when the 50 reduction in performance was identified at each OTO band the. experiment was stopped for that OTO band and testing was continued at the next OTO band The list of HDDs. tested are shown in Table 1,Table 1 Table of 12 HDDs tested. Figure 3 The minimum read and,write speeds as percentage of their.
respective baseline values shown in,OTO frequency bands The perfor. mance of the HDD drops dramatically,after reaching the 50 curve shown. by the black curve with black diamond,data points,Frequency HZ. IMPACT OF SOUND ON COMPUTER HARD DISK DRIVES AND RISK MITIGATION MEASURES. Figure 4 shows the average 50 curve for the 12 different HDDs tested across the 500 Hz to 10 kHz frequency. range The average 50 performance reduction curve indicates that an SPL of approximately 110 dB re 20 Pa in. any OTO band is likely to cause reduced performance in HDDs. However SPL values for some drives within the test samples experienced reduced read write speeds. while exposed to sound as low as 85 dB re 20 Pa,Figure 4 The SPL at one third octave. frequency bands where the perfor,mance of the HDD was reduced by.
50 from the baseline values The plot,in the red shows the average of the. 50 points for 12 different HDDs,Frequency HZ,The Metrics of Measuring and Defining Sound. THE SOURCE PATH RECEIVER PARADIGM, There are several different measurements that can be made and metrics that can be used to quantify sound. amplitude and frequency When investigating noise control problems consider the source path receiver. paradigm represented in Figure 5 a number of filters in order to easily select the specific points within. the system, The source path receiver paradigm provides insight into the measurements necessary to define and address. acoustic issues in data centers The source is a system sub system or component that is generating noise the. path is any combination of acoustic or structural paths the energy can take to travel from the source to the. receiver and the receiver is the person instrument or object that can be affected by the noise Although. this definition may seem simplistic it is a powerful concept to help understand the parameters impacting. acoustic measurements,Figure 5 Source Path Receiver Paradigm.
IMPACT OF SOUND ON COMPUTER HARD DISK DRIVES AND RISK MITIGATION MEASURES. Agent discharge nozzles and detection alarms that are part of inert gas fire suppression systems are. sources of sound If these sources are moved around a room or from room to room they will not. sound the same i e their measured sound pressure levels at a specified distance from the source will. not be constant due to changing path characteristics The SPL measurements cannot be immediately. compared from one room to another unless the path characteristics are known Therefore to correctly. quantify the sound output of a source a sound metric independent of the distance between the source. and receiver and independent of the path must be used This measurement metric is sound power level. dB re 1 picowatt Barnard 2014 Sound power level measures the total acoustic energy per unit time emitted. from a source Unlike sound pressure level sound power level is only a function of the source and is independent of. measurement distance and other path effects,SOUND MEASUREMENT SCALES. As a source emits acoustic power that energy is transmitted through the path to the receiver which may be the. human ear or other mechanical devices depending on the problem being addressed Many SPL measurements. default to the A weighting scale designated by dBA A weighting is frequency dependent and reflects the non. linear response of the human ear at modest sound pressure levels See Figure 6 However a hard disk drive HDD. exposed to sound pressure levels does not react to sound pressure in the same way as a human ear Therefore the. sound pressure level received by a HDD should not be measured in units of dBA but instead an unweighted sound. measurement Z weighting dBZ should be used,Frequency HZ. Figure 6 One third octave band frequency domain depiction of. A and Z weighting, IMPACT OF SOUND ON COMPUTER HARD DISK DRIVES AND RISK MITIGATION MEASURES. NOISE FREQUENCY BANDS, It is important to understand that noise will affect each model or manufacturer of HDDs in unique ways The. varying design of HDDs will result in certain frequencies causing HDD sensitivity due to component vibrations. structural modes The structural modes of each HDD are a key factor in noise induced failure Because of this it. is important to understand the frequency dependent characteristics of both the noise source and the response of. the receiver In room acoustics scientists use logarithmically distributed band limited frequency ranges know as. one third octave OTO bands In addition to the frequency content the noise should also include measurement. of magnitude in terms of dBZ For suppression nozzles the sound power is required to define the magnitude of. the noise generated Nozzle sound power measurement allows for the direct comparison of one nozzle design. to another regardless of the testing environment If suppression nozzles are not characterized by sound power. but rather stated in terms of sound pressure level SPL at a distance from the nozzle the characterization can. be misleading For example there could be significant undisclosed path absorption factors in the test setup that. reduced the reported sound pressure readings captured by a microphone There could also be constructive or. destructive interference in a reflective measurement environment This will mean that the reported performance. will only be valid for a server room set up that is identical to the test set up This will almost never be. DATA CENTER SOUND PRESSURE LEVEL CALCULATIONS, Measuring the sound power level of the nozzle also allows for the use.
of acoustic engineering principles that can more accurately predict the. sound pressure level of a receiver which in the case of data centers. would be the HDD Established acoustic engineering equations require. additional data to define the path characteristics of the room in order. to predict a sound pressure level This data includes the distance. between the source and the receiver and the total acoustic absorption. within the sound path The results determined by using the acoustic. equations can help a designer to select the appropriate nozzle and its. placement HDD placement within a room and the room construction. materials to achieve the desired sound pressure level at the HDDs Data. center owners and operators must consider the source path receiver. paradigm and understand that sound is generated as sound power at a. source and transformed through the room paths to generate the sound. pressure at HDDs Figure 7 shows the model and measurements for a. typical data center using the source path receiver paradigm for the Figure 7 Example of . IMPACT OF SOUND ON COMPUTER HARD DISK DRIVES AND RISK MITIGATION MEASURES 1 Introduction to Data Center Acoustic Sensitivity Data centers are relied upon to store and distribute valuable information from customers across many industries from the investment banking to the healthcare sector This valuable information is primarily stored on Hard Disk Drives HDD Industry demands that data

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