Patent Publication Number: US-2011051581-A1

Title: Vibration analysis methodology using data storage devices

Description:
BACKGROUND 
     Disc drives are digital data storage devices that enable users of computer systems to store and retrieve large amounts of data in a fast and efficient manner. Disc drives of the present generation have data storage capacities in excess of hundreds of gigabytes (GB) and can transfer data at sustained rates of one hundred megabytes (MB) per second or greater. 
     A typical disc drive includes a plurality of magnetic recording discs, which are mounted to a rotating hub of a spindle motor for rotation at a constant, high speed. An array of read/write heads is disposed on adjacent surfaces of the discs to transfer data between the discs and a host computer. The heads are radially positioned over the discs by a rotary actuator and a closed loop, digital servo system, and are caused to fly proximate the surfaces of the discs upon air bearings established by air currents set up by the high speed rotation of the discs. 
     A plurality of nominally concentric tracks are defined on each disc surface. A preamplifier and driver circuit generates write currents that are used by the head to selectively magnetize the tracks during a data write operation and amplifies read signals detected by the head during a data read operation. A read/write channel and interface circuit are operably connected to the preamplifier and driver circuit to transfer the data between the discs and the host computer. 
     Disc drives may be used in a stand-alone fashion, such as in a typical personal computer (PC) configuration, where a single disc drive is utilized as the primary data storage peripheral. Alternatively, in applications requiring great amounts of data storage capacity or high input/output (I/O) bandwidth, a plurality of drives can be arranged into a multi-drive array, such as a RAID (“Redundant Array of Inexpensive Discs”; also “Redundant Array of Independent Discs”). 
     SUMMARY 
     In one example, the disclosure is directed to a method comprising acquiring, by a data storage device, signals generated by at least one sensor that relate to a mechanical vibration of the data storage device, wherein the at least one sensor is in electrical communication with the data storage device, and storing a representation of the signals as data in the data storage device. 
     In another example, the disclosure is directed to a system comprising a data storage device, and at least one sensor that generates signals related to a mechanical vibration of the data storage device, wherein the at least one sensor is in electrical communication with the data storage device, and wherein the data storage device acquires the signals and stores a representation of the signals in the data storage device. 
     In another example, the disclosure is directed to a computer-readable medium comprising instructions that cause a processor in electrical communication with a data storage device to acquire signals generated by at least one sensor that relate to a mechanical vibration of the data storage device, wherein the at least one sensor is in electrical communication with the data storage device, and to store a representation of the signals as data in the data storage device. 
     In another example, the disclosure is direct to a system comprising a data storage device, at least one sensor that generates signals related to a mechanical vibration of the data storage device, wherein the at least one sensor is in electrical communication with the data storage device, and wherein the data storage device acquires the signals and stores a representation of the signals in the data storage device, and a chassis configured to support a plurality of data storage devices. 
     These and various other features and advantages will be apparent from a reading of the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of an example data storage device that may be used for evaluation of cabinet rotational vibration (RV) and linear vibration (LV) characterization and adverse resonance identification in accordance with this disclosure. 
         FIG. 2  is an outline plan view of a printed circuit board assembly of the data storage device of  FIG. 1  having a sensor attached thereto in accordance with this disclosure. 
         FIG. 3  is a front view of an example cabinet configured to support a plurality of data storage devices. 
         FIG. 4  is a conceptual block diagram illustrating one example data storage device configured to act as a data acquisition system, in addition to being a data storage device. 
         FIG. 5  depicts a graph illustrating one example of a position error signal that may be captured and recorded using the techniques of this disclosure. 
         FIG. 6  depicts a graph illustrating a position error signal after a transform has been performed on the signal. 
         FIG. 7  depicts a graph illustrating rotational vibration data measured with accelerometers mounted external to a data storage device. 
         FIG. 8  is a flow chart illustrating an example method for using a data storage device as a data acquisition system for linear vibration data and rotation vibration data, in addition to being a storage device. 
     
    
    
     DETAILED DESCRIPTION 
     In general, this disclosure describes techniques for using the data storage device under evaluation for cabinet rotational vibration (RV) and linear vibration (LV) characterization and adverse resonance identification. By using the data storage device itself as an instrument for detecting resonant frequencies, a customer&#39;s data storage device acceptance qualification time may be improved. By improving a customer&#39;s drive acceptance qualification time, time-to-market may be decreased for both the data storage device supplier and the customer. In addition, using the data storage device itself as an instrument for detecting resonant frequencies may increase the amount of information available to design teams and engineers, e.g., the cabinet design team and servo engineers. Further, using the data storage device itself as an instrument for detecting resonant frequencies simplifies and reduces the time required to perform the traditional method of measuring vibration using accelerometers attached to the outer casing of the data storage device, e.g., a disc drive. Further still, using the data storage device itself to detect resonant frequencies automates a data collection process that was previously labor intensive and time consuming. 
     As mentioned above, disc drives may be used in a stand-alone fashion, such as in a typical personal computer (PC) configuration where a single disc drive is utilized as the primary data storage peripheral. Alternatively, in applications requiring great amounts of data storage capacity or high input/output (I/O) bandwidth, a plurality of drives can be arranged into a multi-drive array, such as a RAID (“Redundant Array of Inexpensive Discs”; also “Redundant Array of Independent Discs”). When one or more drives are used in a multi-drive array, fans and other devices mounted within the chassis in which the drive(s) are mounted may cause resonances that stimulate the chassis, thereby causing the chassis and the drive(s) to vibrate. High vibration levels adversely affect disc drive operation. 
     The traditional method of using accelerometers to measure the vibration is often not practical, and sometimes not possible, because the space allowed between multiple drives or other hardware in a cabinet, for example, may be too small to allow accelerometers to be placed on the outer casing of the data storage device without modifying the conditions of the cabinet itself. Of course, modifying the cabinet to allow for accelerometers and other test equipment changes the test conditions and, as such, is not an accurate representation of the system. Further still, the traditional method of using accelerometers is often limited to measuring vibrations on a small number of drives due to channel limitations of the test equipment. 
       FIG. 1  shows an illustration of one example of data storage device  100  that may be used as an instrument for cabinet rotational vibration (RV) and linear vibration (LV) characterization and adverse resonance identification. In the example shown in  FIG. 1 , data storage device  100  is illustrated as a hard disc drive. However, it shall be understood that other types of data storage devices may also be used, and that the specific embodiment shown and described herein is for illustrative purposes only and is not a limitation of the present invention. For example, data storage device  100  may be a magnetic disc drive, optical disc drive, solid-state drive, or another device. 
     Disc drive  100  includes base  102  to which various components of disc drive  100  are mounted. Top cover  104 , shown partially cut away, cooperates with base  102  to form an internal, sealed environment for the disc drive in a conventional manner. The components include spindle motor  106  that rotates one or more discs  108  at a constant high speed. Information is written to and read from tracks on discs  108  through the use of an actuator assembly  110 , which rotates during a seek operation about bearing shaft assembly  112  positioned adjacent discs  108 . Actuator assembly  110  includes a plurality of actuator arms  114  that extend towards discs  108 , with one or more flexures  116  extending from each of actuator arms  114 . Mounted at the distal end of each of flexures  116  is read/write head  118  which includes an air bearing slider (not shown) enabling head  118  to fly in close proximity above the corresponding surface of the associated disc  108 . 
     During a seek operation, the position of read/write heads  118  over discs  108  is controlled through the use of voice coil motor (VCM)  124 , which typically includes coil  126  attached to actuator assembly  110 , as well as one or more permanent magnets  128  which establish a magnetic field in which the coil  126  is immersed. The controlled application of current to coil  126  causes magnetic interaction between permanent magnets  128  and coil  126  so that coil  126  moves in accordance with the well known Lorentz relationship. As coil  126  moves, actuator assembly  110  pivots about bearing shaft assembly  112 , and heads  118  are caused to move across the surfaces of discs  108 . 
     Flex assembly  130  provides the requisite electrical connection paths for actuator assembly  110  while allowing pivotal movement of actuator assembly  110  during operation. The flex assembly includes printed circuit board  132  to which head wires (not shown) are connected. The head wires are routed along actuator arms  114  and flexures  116  to heads  118 . Printed circuit board  132  typically includes circuitry for controlling the write currents applied to heads  118  during a write operation and a preamplifier for amplifying read signals generated by the heads  118  during a read operation. The flex assembly terminates at flex bracket  134  for communication through base deck  102  to a disc drive printed circuit board (not shown) mounted to the bottom side of disc drive  100 . 
     As shown in  FIG. 1 , located on the surface of discs  108  are a plurality of nominally circular, concentric tracks  109  (only one of which is shown). Each track  109  preferably includes a number of servo fields that are periodically interspersed with user data fields along the track  109 . The user data fields are used to store user data and the servo fields used to store servo information used by a disc drive servo system to control the position of the read/write heads. 
       FIG. 2  is an outline plan view of an example printed circuit board assembly (PCBA) of the data storage device of  FIG. 1 . In one example, PCBA  200  or  132  may include a processor  202 , memory device  204 , buffer  206 , motor driver  208 , and at least one sensor  210 A and/or  210 B. Sensors  210 A and  210 B need not be the same type of sensor. It should be noted that the positioning and x-y orientation of processor  202 , memory device  204 , buffer  206 , and motor driver  208  depicted in  FIG. 2  is for ease of illustration purposes only and is in no manner meant to suggest a particular layout of the devices. 
     Processor  202  may be configured to perform a number of tasks, including controlling VCM  124  in order to move head  118  across the surface of discs  108 , directing head  118  to read data from or write data to disc  108 , and transmitting the data between data storage device  100  and the central processing unit (CPU) of a computer (not shown) in communication with data storage device  100 . 
     Memory device  204  may be configured to store instructions executable by processor  202 . While memory device  204  is shown as a separate device in  FIG. 2 , in some examples, memory device  204  is integral with processor  202 . Memory device  204  may include read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), and flash memory, for example. 
     Buffer  206  may be a random access memory (RAM) device configured to temporarily store data that is frequently accessed by the drive, thereby potentially increasing the data transfer rate between data storage device  100  and the computer, and reducing the wear on the discs  108 . 
     Motor driver  208  is an integrated circuit device that amplifies the current from processor  202 . By itself, processor  202  may not source enough current to drive VCM  124 . As such, PCBA  200  may include motor driver  208  which amplifies signals received from processor  202  in order to drive VCM  124 . 
     Exposure to shock and vibration may adversely affect the integrity of data storage device  100 . Disc drives are particularly susceptible to high vibration levels. For example, elevated rotational vibration levels may decrease data transfer rates, comprise data integrity, or result in permanent damage to the storage medium. In order to detect rotational vibration, linear vibration, and/or shock to data storage device  100 , PCBA  200  further includes one or more sensors  210 A and/or  210 B. 
     Sensors  210 A and/or  210 B may be rotational vibration (RV), linear vibration (LV), and/or shock sensors mounted on PCBA  200  and in electrical communication with processor  202 . In some examples, sensors  210 A and/or  210 B may be a micro-electromechanical system, or MEMS, based device. In one specific example, sensors  210 A and/or  210 B may be MEMS-based linear vibration sensors such as the LIS3LV02DL three-axis linear accelerometer available from ST Microelectronics. In one example, the vibration sensor may be an accelerometer. 
     In some examples, linear vibration sensors may be used to calculate the rotational vibration of data storage device  100 . For example, as seen in  FIG. 2 , sensors  210 A and  210 B are oriented with respect to an x-y axis such that any motion of PCBA  200 , and thus data storage device  100 , will include both an x-component and a y-component. Processor  202  may then execute an algorithm stored in memory  204 , for example, that determines the rotational vibration of data storage device  100  based on the x and y components of motion measured by sensors  210 A and/or  210 B. It should be noted that two or more sensors may be needed in order to calculate the rotational vibration of data storage device  100 . 
     In addition, PCBA  200  may include other sensors that are in place of or in addition to the LV, RV, and/or shock sensors  210 A and/or  210 B. In one example, PCBA  200  may include temperatures sensors for measuring the temperature of data storage device  100 . In another example, PCBA  200  may include a humidity sensor for measuring the humidity within data storage device  100 . Processor  202  may periodically record to data storage device  100  the temperature and humidity conditions present within data storage device  100 , thus providing additional information that may be useful in resolving any fault conditions that may occur. 
       FIG. 3  is a front view of cabinet  240  configured to support a plurality of data storage devices  100 . Cabinet  240  includes a frame system  242  that may divide the cabinet into a plurality of quadrants  243 A-C, with each quadrant configured to support a plurality of data storage devices  100 . For ease of illustration, cabinet  240  in  FIG. 3  is depicted with only a single quadrant  243 A supporting three data storage devices, namely data storage devices  100 A,  100 B, and  100 C. As will be discussed in more detail below, cabinet  240  may further include light-emitting diodes (LEDs) to provide a visual indication of an error condition, for example, to an operator monitoring operation or testing of the data storage devices  100 .  FIG. 3  depicts three LEDs,  244 A,  244 B, and  244 C (collectively, “LEDs  244 ”) to provide visual indication of an error condition for corresponding storage devices  100 A,  100 B,  100 C, for example. In some examples, a quadrant, e.g., quadrant  243 A, may include only a single LED  244  to provide visual indication of an error in any of data storage devices  100 A,  100 B, and  100 C. 
     Although not depicted in  FIG. 3 , cabinet  240  may further include fans and other devices that act as vibration driving forces. The frequency of these driving forces may stimulate cabinet  240 , and thus any data storage devices  100  attached to cabinet  240 , to vibrate. If the frequency of these driving forces corresponds with any resonant frequency of data storage device  100 , the resulting resonance in the data storage device may compromise the read/write integrity of the data storage device, the servo system of the drive, or the like. As such, it is desirable to identify and quantify adverse resonances and frequencies that are associated with degraded storage device performance or other storage device issues. 
     In accordance with this disclosure, RV, LV, and/or shock sensors  210 A and/or  210 B mounted on PCBA  200  of data storage device  100  may be used in conjunction with logging technologies, e.g., logging software, to allow data storage device  100  to monitor and capture data representative of the adverse resonances and frequencies that are associated with degraded storage device performance or other device issues. By using sensors  210 A and/or  210 B in conjunction with logging technologies, data storage device  100  may be used as a tool to log any resonance present in the cabinet. Thus, data storage device  100  is transformed from simply a storage medium to a sensing mechanism to aid in qualifying and modifying the design of a cabinet. 
     Logging software capable of capturing data representing frequency signals present in cabinet  240  may be stored on data storage device  100 . For example, in one example, the logging software may include two complimentary modules of monitoring technologies. A first module of monitoring technology may provide for a low sample, periodic accumulation of data for as long a period as desired, including for the life of data storage device  100 . In one example, the data may be, for example, linear vibration (LV) data generated by sensors  210 A and/or  210 B that is converted by processor  202  via an algorithm stored in memory  204  to rotational vibration (RV) data. In other examples, the data may be RV data that is generated directly by sensors  210 A and/or  210 B. In either case, the first module of monitoring technology may record the RV data to disc  108 . For example, the magnitude of RV encountered by data storage device  100  during its operation may be recorded to disc  108 . The magnitude of RV encountered may then be compared with an RV profile of data storage device  100 , thereby allowing processor  202  to determine whether data storage device  100  conforms with the product specification. 
     In some cases it may be desirable for the first module to include instructions that cause processor  202  to record the absolute mean of the RV data over specific periods of time, e.g., an average of RV data over a fixed or predetermined amount of time, to disc  108 . Instead of or in addition to recording the absolute mean of the RV data, it may be desirable for the first module to be include instructions that, when executed, cause processor  202  to record the maximum absolute mean of the RV data, e.g., the highest value of RV sensed in the last sample, to disc  108 . 
     In some examples, this first module of monitoring technology may allow a user to change the sampling rate, either manually or automatically. For instance, the sampling rate may be set at one hour, but be configurable to sample at four minutes or lower. Of course, increasing the sampling rate in this manner results in a large amount of information in a short period of time, thereby reducing the time needed to gather the frequency information necessary to resolve any potential design issues. One specific example of monitoring technology that may be used is Self-Monitoring, Analysis, and Reporting Technology (“SMART”). 
     SMART logging technology may allow a “threshold” to be set in order to determine design margins and boundary conditions associated with the cabinet design. For example, using SMART, a threshold may be set for either or both an RV and LV condition. When either the RV or LV condition is violated, e.g., the recorded data exceeds the threshold, the SMART technology may produce a warning that informs the host of the violation. 
     A second module of monitoring technology may also be used for logging purposes. Unlike the first module, e.g., SMART technology, the second module of monitoring technology may be used for an event-driven capture of information. If an error condition occurs, the second module of monitoring technology may capture more details of events than the first module. One specific example of monitoring technology that may be used is the Unified Debug System (“UDS”) logging technology. For example, during an error condition, the UDS logging may automatically record the frequency content, the LV and x-y coordinates from sensors  210 A and/or  210 B, the RV (after the RV has been calculated from the LV and x-y coordinates, or measured by RV sensors), and a time-stamp (day and time) indicating when the error condition occurred. 
     Each data storage device  100  present within cabinet  240  may record the time-stamp, thus allowing any data recorded on data storage devices  100  to be time-aligned. Time-alignment may be useful in determining that a particular condition present within cabinet  100  at a given time affected only a particular set of data storage devices  100 , or all data storage devices  100 . For example, during an error condition, the second module of monitoring technology may cause processor  202  to record a time stamp for all drives present within cabinet  240  of  FIG. 3 , thereby indicating that an error condition occurred. The second module may then cause processor  202  to record the error data to the particular drives in which the error condition occurred. At a later time when the error data is retrieved and time-aligned, it may be determined, for example, that only the data storage devices located in quadrant  243 A, for example, of cabinet  240  recorded an error condition at the time indicated by the time stamp. Using this information, combined with the frequency information recorded, it may determined that a cooling fan, for example, located in quadrant  243 A of cabinet  240  turned on at that time, and as such, may be the cause of the adverse resonance condition that produced the recorded error. 
     In some examples, the first module of logging technology may issue a command to the second module of logging technology in order to begin logging data. In other examples, a command to the second module of logging technology to begin logging may be an instruction issued by processor  202  as part of the general error recovery procedures used by data storage device  100 . 
     In one example, the second module of logging technology may include position error signal (PES) sampling. PES sampling may allow data storage device  100  to capture the frequency components introduced by cabinet  240 . That is, PES sampling provides a tool that enables data storage device  100  to record frequencies present within the bandwidth of the servo system of data storage device  100 . PES sampling may allow, for example, processor  202  to determine whether data storage device  100  is beyond the data storage device&#39;s on-cylinder limit, i.e., beyond the limit at which data storage device  100  can stay on a track. The on-cylinder limit, in some examples, may be an upper and lower limit, each represented by a percentage, e.g., an upper limit of +16% and a lower limit of −16%. In one example, the second module may capture and store a number of position error signal sample points. In some examples, the position error signal is recorded along with the segment and position information, e.g., the wedge number of the data storage unit. Once these sample points are recorded, a transform, e.g., fast Fourier transform (FFT), discrete Fourier transform (DFT), or other similar transform that converts data representing a signal to the frequency domain, may be performed on the recorded data in order to determine the frequency content of the vibrations present within the system. Once the frequency content of the vibrations is determined, a design engineer may use this frequency information to aid in investigating the source of the resonance present within cabinet  240 . For example, the frequency information may lead an engineer to determine that the source of the resonance was a cooling fan or some other hardware present within cabinet  240 . 
     In some examples, the second module may record additional information related to the error, e.g., the error generated by excessive vibration. The second module may record an error code that indicates the error type, e.g., hardware error. The second module may also record the trigger capture mechanism by which the error was captured, e.g., read-recovery operation, write-recovery, and UDS logging. The second module may also record the servo firmware version and/or the interface firmware version. As mentioned above, the time at which the error occurred may be recorded via a time stamp. In addition, the second module may also record the power cycle count. The second module may also record the number of captures within a data set in an index, for example. The second module may also record the location of the data storage device where the error occurred, e.g., a logical block address. Of course, these are just some non-limiting examples of the information that may be recorded. Other examples not specifically mentioned are nevertheless considered to form part of this disclosure. 
     The logging features of the first module and the second module may be turned on and turned off, or invoked, via a switch, for example. In some examples, the switch may be turned on or off via mode pages, e.g., using Serial Attached SCSI (“SAS”)/Fiber Channel and SCSI. That is, a customer, for example, may modify the mode page settings of the data storage device such that the data storage device will operate as a standard drive, or in accordance with the techniques of this disclosure, as a data acquisition system for LV, RV, shock, temperature, humidity, or the like. Mode page is a method that reports and modifies configurational changes within a data storage device. In one example, setting the mode page may include setting a bit. The bit may be set via hardware or software. 
     In other examples, e.g., AT Attachment (ATA), the logging may be turned on by using SMART command transport (SCT) protocol with a unique action code and function code value that allows similar functional behavior. That is, an SCT command may be sent to a data storage device having an ATA interface using a specific action code. SCT action codes are analogous to mode page settings and allow reporting of and modification to the configuration of the data storage device. 
       FIG. 4  is a conceptual block diagram illustrating one example data storage device  100  configured to act as a data acquisition system, in addition to being a data storage device. In  FIG. 4 , processor  202  is depicted as being in electrical communication with disc  108 , sensors  210 A and/or  210 B (shown as “sensors  210 ” for simplicity), memory  204 , and LEDs  244 . Stored within memory  204  are the first module  250 , or low sample rate module, of monitoring technology, and the second module  252 , or event driven module, of monitoring technology. In one specific example, first module  250  may comprise SMART technology and second module  252  may comprise UDS logging technology. First module  250  and second module  252  are depicted as separate modules. However, it should be noted that in some examples, the two modules may be combined into a single module that includes the features of both the first module and the second module. 
     Processor  202  is also in electrical communication with sensors  210 A and/or  210 B. Sensors  210 A and/or  210 B may include rotational vibration (RV), linear vibration (LV), and/or shock sensors. Sensors  210 A and/or  210 B may also include numerous other types of sensors that may be used to collect information relevant to error conditions. For example, sensors  210 A and/or  210 B may be temperature sensors, humidity sensors, or the like. 
     Processor  202  is also in electrical communication with LEDs  244 . The dotted line around LEDs  244  in  FIG. 4  indicates that the LEDs may be located on data storage device  100 , on cabinet  240 , or both. LEDs  244  may provide a visual indication as a warning to an operator, technician, engineer, or other personnel monitoring the data storage devices stored within cabinet  240  that an error condition has occurred. For example, LEDs  244 A-C may provide a visual indication to the person monitoring the testing of data storage devices  100 A-C if an RV threshold is exceeded in the corresponding data storage devices  100 A-C. For ease of illustration purposes, LED driver circuitry that may be required to pulse LEDs  244  has not been depicted. In some examples, in addition to or instead of a visual indication, an aural indication, e.g., via a speaker, may be provided in order to warn of an error condition, e.g., exceeding a threshold. 
     Processor  202  is also in electrical communication with disc  108  of data storage device  100 . Information received by processor  202  via sensors  210 A and/or  210 B is written to a portion of disc  108 . As non-limiting examples, vibration and shock data, as well as temperature and humidity data may be written to disc  108 . In some examples, the portion of disc  108  in which the information is written may be a predefined area, e.g., a specific sector. In other examples, the portion of disc  108  may be the first sector of the disc or the last sector of the disc. In examples in which data storage device  100  is a solid-state drive, the portion in which information from sensors  210 A and/or  210 B is written may be predefined page or erasure block. 
       FIG. 5  depicts a graph illustrating one example of a position error signal (PES) that may be captured and recorded using the techniques of this disclosure.  FIG. 5  plots the data samples representing position error signal  300  captured and recorded to data storage device  100  and, in particular, second module  252 . The x-axis is the wedge number of data storage device  100  and the y-axis is a percentage of head  118  being off track, e.g., 0.1 is 10% off track, where  302  and  304  represent the boundaries for the head to be considered on track, i.e., the on-cylinder limit. In particular,  FIG. 5  illustrates how position error signal  300  varies across the wedges of data storage device  100 . 
       FIG. 6  depicts a graph illustrating position error signal (PES)  300  of  FIG. 5  after a transform, e.g., a fast Fourier transform, has been performed on the signal. In other words,  FIG. 6  is graph illustrating position error signal  300  of  FIG. 5  represented in the frequency domain. The y-axis represents the magnitude, or energy, of position error signal  300  (“PES magnitude”) and the x-axis represents frequency in Hertz (Hz). As seen in  FIG. 6 , most of the energy of PES signal  300 , i.e., the higher PES magnitudes, occurs at lower frequencies, e.g., at or below about 500 Hz, as shown at  306 . 
       FIG. 7  depicts a graph illustrating rotational vibration data measured with accelerometers mounted external to data storage device  100 , e.g., to top cover  104 . The y-axis represents the magnitude of the rotational vibration in (rad/s 2 ) 2 /Hz and the x-axis represents frequency in Hz. As seen in  FIG. 7 , the highest magnitudes of the rotational vibration measurement  400 , indicated by  402  and  404 , occur at lower frequencies, e.g., below about 500 Hz. The results shown in  FIG. 7  correspond with the results shown in  FIG. 6 . That is, both graphs illustrate that frequencies below about 500 Hz should be investigated as a source of system resonance. 
       FIG. 8  is a flow chart illustrating an example method for using a data storage device as a data acquisition system for LV and RV, in addition to being a storage device. In the method illustrated in  FIG. 8 , data storage device  100 , via processor  202  executing instructions, e.g., from first module  250 , acquires signals generated by one or more sensors  210 A and/or  210 B in electrical communication with data storage device  100  that relate to a mechanical vibration of data storage device  100  ( 500 ). In one example, data storage device may begin acquiring signals in response to modification, e.g., by a customer, of a mode page setting by the changing a bit, for example. In another example, the data storage device may begin acquiring signals in response to receiving specific action code, e.g., an SCT command may be sent to a data storage device having an ATA interface using a specific action code. Sensors  210 A and/or  210 B may be, for example, linear vibration sensors, humidity sensors, temperature sensors, and accelerometers. Data storage device  100  may be, for example, a magnetic disc drive, an optical disc drive, a solid-state drive, or another storage device. In one example, two or more sensors may be necessary, wherein each of the two or more sensors is configured to detect rotational vibration in data storage device  100 . Data storage device  100  then stores a representation of the signals as data in data storage device  100  ( 502 ). In some examples, the data comprises rotational vibration data. 
     In one example, processor  202  compares the data stored to a threshold value, e.g., an RV profile of data storage device  100 , and provides a warning, e.g., a visual indication via LEDs  244 , if the data exceeds the threshold value. 
     In some examples, if the data exceeds the threshold value, processor  202  may execute instructions, e.g., from second module  252 , that store additional data, e.g., the frequency content, the LV and x-y coordinates from sensors  210 A and/or  210 B, the RV (after the RV has been calculated from the LV and x-y coordinates, or measured by RV sensors), and a time-stamp (day and time) indicating when the error condition occurred. Processor  202  may compare the additional data to at least one limit, e.g., an on-cylinder limit, and perform a transform, e.g., a fast Fourier transform, on the additional stored data to transform the data into a different domain, e.g., the frequency domain, and store the transformed data to data storage device  100 . Processor  202  may compare the transformed data to a rotational vibration profile of the data storage, e.g., an RV profile required by the product specifications. If processor  202  determines that the transformed data is outside the profile, e.g., the energy or magnitude of the signal exceeds the product specification, then processor  202  may store an error code in the data storage device, servo data, UDS, or error logging data. 
     The techniques described in this disclosure may be implemented, at least in part, in hardware, software, firmware or any combination thereof. For example, various aspects of the described techniques may be implemented within one or more processors, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. The term “processor” or “processing circuitry” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry. A control unit comprising hardware may also perform one or more of the techniques of this disclosure. 
     Such hardware, software, and firmware may be implemented within the same device or within separate devices to support the various operations and functions described in this disclosure. In addition, any of the described units, modules or components may be implemented together or separately as discrete but interoperable logic devices. Depiction of different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized by separate hardware or software components. Rather, functionality associated with one or more modules or units may be performed by separate hardware or software components, or integrated within common or separate hardware or software components. 
     The techniques described in this disclosure may also be embodied or encoded in a computer-readable medium, such as a computer-readable storage medium, containing instructions. Instructions embedded or encoded in a computer-readable medium may cause a programmable processor, or other processor, to perform the method, e.g., when the instructions are executed. Computer readable storage media may include random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), flash memory, a hard disk, a CD-ROM, a floppy disk, a cassette, magnetic media, optical media, or other computer readable media. 
     The implementations described above and other implementations are within the scope of the following claims.