# Patent

## Title
Read failover method and apparatus for a data storage system

## Abstract

A reader failover system and method are described for a data storage system. At least two reader systems, including a first reader element and a second reader element, situated on the same head, are employed to read a magnetic storage medium. In an aspect, the head is a two-dimensional magnetic recording (TDMR) head. Control circuitry detects when the first reader system provides less than a predetermined performance or fails, and thereafter causes the second reader system, but not the first reader system, to read the magnetic storage medium. In an aspect, a buffer stores a first reader element signal until the control circuitry detects whether or not the first reader element provides less than a predetermined performance or fails. In an aspect, when a reader element fails, data recovery is performed, and all of, or a majority of, the media continues to be readable, improving the data storage system robustness.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to provisional U.S. Patent Application Ser. No. 62/005,796, filed on May 30, 2014, which is hereby incorporated by reference in its entirety.


BACKGROUND
Magnetic storage systems are utilized in a wide variety of devices in both stationary and mobile computing environments. Magnetic storage systems include hard disk drives (HDD), and solid state hybrid drives (SSHD) that combine features of a solid-state drive (SSD) and a hard disk drive (HDD). Examples of devices that incorporate magnetic storage systems include desktop computers, portable notebook computers, portable hard disk drives, servers, network attached storage, digital versatile disc (DVD) players, high definition television receivers, vehicle control systems, cellular or mobile telephones, television set top boxes, digital cameras, digital video cameras, video game consoles, and portable media players.
There is an ongoing effort within the magnetic storage system industry to increase storage capacity while maintaining the same external drive form factor. Track density has increased, and track pitch has decreased, such that magnetic read heads may detect more inter-track noise. Two-dimensional magnetic recording (TDMR) uses multiple read heads to read a single data track, and can improve the reading performance of a magnetic storage system with a high-density disk, as compared to a system using a single read head.



BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing aspects and many of the attendant advantages described herein will become more readily appreciated by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
FIG. 1 is a top plan view of a disk drive data storage system in which embodiments are useful;
FIG. 2 is a top plan view of a data storage disk, showing servo tracks and servo sectors;
FIG. 3 is a top plan view of a hard disk drive (HDD) including a head and a disk including servo tracks, servo sectors, and control circuitry operable to actuate the head over the disk, in an embodiment;
FIG. 4 is a flow diagram illustrating a reader failover system and method for a data storage system, in an embodiment;
FIG. 5 is a schematic representation of a reader failover apparatus including a read channel with two reader element inputs, and control circuitry, as can be used in a data storage system as in FIG. 1, in an embodiment; and
FIG. 6 is a sectional view representation illustrating components of a system that executes methods of an embodiment.



DETAILED DESCRIPTION
In the following description, numerous specific details are disclosed to provide a thorough understanding of embodiments of the method, system and apparatus. One skilled in the relevant art will recognize, however, that embodiments of the method, system and apparatus described herein may be practiced without one or more of the specific details, or with other electronic devices, methods, components, and materials, and that various changes and modifications can be made while remaining within the scope of the appended claims. In other instances, well-known electronic devices, components, structures, materials, operations, methods, process steps and the like may not be shown or described in detail to avoid obscuring aspects of the embodiments. Embodiments of the apparatus, method and system are described herein with reference to figures.
Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, electronic device, method or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may refer to separate embodiments or may all refer to the same embodiment. Furthermore, the described features, structures, methods, electronic devices, or characteristics may be combined in any suitable manner in one or more embodiments.
Magnetic storage system performance demands and design needs have intensified. The current demand for larger capacity in a smaller dimension is linked to the demand for ever increasing storage track density. As the density of data on a magnetic storage medium increases, the strength of the magnetic fields generally decrease, in order to minimize interference. With an increase in track density and decrease in track pitch, magnetic read heads may detect more inter-track noise. Two-dimensional magnetic recording (TDMR) can improve the reading performance of a magnetic storage system with a high-density disk, as compared to a system using a single read head. TDMR read heads counteract extraneous noise by using multiple read elements to read a single data track, and as such, help to create a better signal to noise ratio (SNR) during read back. Additionally, using TDMR, two or more tracks may be detected simultaneously.
However, with a conventional TDMR system with multiple read elements, or a single reader system, an entire media surface may be lost when a reader element fails. Reader element failure may occur for a wide variety of reasons, including being exposed to damaging environmental conditions. As an example, one reader element situated on the same head as a second reader element may react differently to particular temperature and humidity, causing failure or substandard performance of one reader element but proper performance by the second reader element on the same head.
A reader failover apparatus, system and method are described herein for a data storage system. Embodiments detect when a first reader system provides less than a predetermined performance or fails. Thereafter, embodiments cause a second reader system, but not the first reader system, to read the magnetic storage medium. A head includes both the first reader element and the second reader element. When the first reader system is determined to properly operate at a predetermined performance, both the first reader system and the second reader system are together utilized to read the magnetic storage medium. In an alternative embodiment, the second reader system is only employed in lieu of the first reader system, when the first reader system is determined to provide less than a predetermined performance or fails.
At least two reader systems are employed to read the magnetic storage medium. In an embodiment, a buffer stores a signal from a first reader element until control circuitry detects whether or not the first reader element provides less than a predetermined performance or fails. In an embodiment, if the first reader element provides less than a predetermined performance or fails, a second reader element, situated on the same head as the first reader element, performs data storage device functions (e.g., data recovery), improving the robustness of a data storage system.
In an embodiment, the methods and apparatus are utilized with a TDMR head. A conventional TDMR drive system selects specific reader elements for normal operation as a function of armature skew angle, servo performance, etc. Reader element selection may also be based on format/error correction capability as determined during drive manufacturing. These functions may be utilized in part by some embodiments described herein.
In an embodiment, all of, or a majority of, magnetic recording media continues to be readable when a reader element fails, as compared to a conventional single reader system or a conventional TDMR system where at least some recording media is not readable when a reader element fails.
The apparatus, system and methods disclosed may be utilized, in an embodiment, with disk drive memory systems, and other memory systems utilizing a magnetic reading device, including a HDD and a SSHD.
Referring to the figures wherein identical reference numerals denote the same elements throughout the various views, FIG. 1 illustrates a disk drive storage system 10, in which embodiments are useful. Features of the discussion and claims are not limited to this particular design, which is shown only for purposes of the example.
Disk drive 10 includes one or more data storage disks 14 of computer-readable data storage media. Typically, both of the major surfaces of each data storage disk 14 include a plurality of concentrically disposed tracks for data storage purposes, including user data sectors and servo sectors. Each data storage disk 14 is mounted on a hub or spindle 16, which in turn is rotatably interconnected with a base plate 12 and/or cover. Multiple data storage disks 14 are typically mounted in vertically spaced and parallel relation on the spindle 16. A spindle motor 18 rotates the data storage disks 14 at an appropriate rate.
The disk drive 10 also includes an actuator arm assembly 24 that pivots about a pivot bearing 22, which in turn is rotatably supported by the base plate 12 and/or cover. The actuator arm assembly 24 includes one or more individual rigid actuator arms 26 that extend out from near the pivot bearing 22. Multiple actuator arms 26 are typically disposed in vertically spaced relation, with one actuator arm 26 being provided for each major data storage surface of each data storage disk 14 of the disk drive 10. Other types of actuator arm assembly configurations may be utilized as well, such as an assembly having one or more rigid actuator arm tips or the like that cantilever from a common structure. Movement of the actuator arm assembly 24 is provided by an actuator arm drive assembly, such as a voice coil motor 20 or the like. The voice coil motor (VCM) 20 is a magnetic assembly that controls the operation of the actuator arm assembly 24 under the direction of control electronics 40.
A suspension 28 is attached to the free end of each actuator arm 26 and cantilevers therefrom. The slider 30 is disposed at or near the free end of each suspension 28. What is commonly referred to as the read/write head (e.g., transducer) is mounted as a head unit 32 under the slider 30 and is used in disk drive read/write operations. As the suspension 28 moves, the slider 30 moves along arc path 34 and across the corresponding data storage disk 14 to position the head unit 32 at a selected position on the data storage disk 14 for the disk drive read/write operations. When the disk drive 10 is not in operation, the actuator arm assembly 24 may be pivoted to a parked position utilizing ramp assembly 42. The head unit 32 is connected to a preamplifier 36 via head wires routed along the actuator arm 26, which is interconnected with the control electronics 40 of the disk drive 10 by a flex cable 38 that is typically mounted on the actuator arm assembly 24. Signals are exchanged between the head unit 32 and its corresponding data storage disk 14 for disk drive read/write operations.
The data storage disks 14 comprise a plurality of embedded servo sectors each comprising coarse head position information, such as a track address, and fine head position information, such as servo bursts. As the head 32 passes over each servo sector, a read/write channel (or servo control system) processes the read signal emanating from the head to demodulate the position information. The control circuitry processes the position information to generate a control signal applied to the VCM 20. The VCM 20 rotates the actuator arm 26 in order to position the head over a target track during the seek operation, and maintains the head over the target track during a tracking operation.
The head unit 32 may utilize various types of read sensor technologies such as anisotropic magnetoresistive (AMR), giant magnetoresistive (GMR), tunneling magnetoresistive (TMR), other magnetoresistive technologies, or other suitable technologies.
FIG. 2 shows a conventional disk format 200 including a number of servo tracks 204 defined by servo sectors 2060-206N recorded around the circumference of each servo track. Each servo sector 206, includes a preamble 208 for storing a periodic pattern, which allows proper gain adjustment and timing synchronization of the read signal, and a sync mark 210 for storing a special pattern used to symbol synchronize to a servo data field 212. The servo data field 212 stores coarse head positioning information, such as a servo track address, used to position the head over a target data track during a seek operation. Each servo sector 206, further includes groups of servo bursts 214 (e.g., N and Q servo bursts), which are recorded with a predetermined phase relative to one another and relative to the servo track centerlines. The phase based servo bursts 214 provide fine head position information used for centerline tracking while accessing a data track during write/read operations. A position error signal (PES) is generated by reading the servo bursts 214, wherein the PES represents a measured position of the head relative to a centerline of a target servo track. A servo controller processes the PES to generate a control signal applied to a head actuator (e.g., a voice coil motor) in order to actuate the head radially over the disk in a direction that reduces the PES.
Referring to FIG. 3, a portion of hard disk drive (HDD) is illustrated, according to an embodiment, including a head 316 and a disk 318. The disk 318 includes a plurality of servo tracks 320, wherein each servo track includes a plurality of servo sectors 3220-322N. The disk drive further includes control circuitry 324 including a servo control system operable to actuate the head over the disk in response to the servo sectors 3220-322N. The disk is rotated by a spindle motor 346 at a rotational speed that is controlled by the control circuitry 324, for example, a motor driver of the control circuitry 324.
Control circuitry 324 processes a read signal 332 emanating from the head 316 to demodulate the servo sectors 3220-322N and generate a position error signal (PES) representing an error between the actual position of the head and a target position relative to a target track. In an embodiment, the target track includes a target data track defined relative to the servo tracks 320, wherein the data tracks may be recorded at the same or different radial density than the servo tracks 320. The control circuitry 324 filters the PES using a suitable compensation filter to generate a control signal 334 applied to a voice coil motor (VCM) 336, which rotates an actuator arm 338 about a pivot in order to actuate the head 316 radially over the disk 318 in a direction that reduces the PES. The control circuitry 324 may also generate a control signal 340 applied to a microactuator 342 in order to actuate the head 316 over the disk 318 in fine movements. Any suitable microactuator 342 may be employed in the embodiments, such as a piezoelectric actuator. In addition, the microactuator 342 may actuate the head 316 over the disk 318 in any suitable manner, such as by actuating a suspension relative to the actuator arm, or actuating a slider relative to the suspension. The servo sectors 3220-322N may include any suitable head position information, such as a track address for coarse positioning and servo bursts for fine positioning. The servo bursts may include any suitable pattern, such as an amplitude based servo pattern or a phase based servo pattern.
To accomplish reading and writing of data to and from the disk, the control circuitry may include a read channel configured to process the read signal 332 from the head 316 and a write channel to prepare write signal 332 for sending to the head 316 for writing.
In an embodiment, head 316 is a TDMR head with multiple reader elements, allowing extraction of multiple read signals and subsequently improved SNR gains via signal processing the signal from multiple reader elements. The reader elements read the same track or adjacent tracks. In an embodiment, TDMR gains are provided when reading mostly the same track or processing signal from a main track and its adjacent tracks. In an embodiment, head 316 is a TDMR head that may be used with tracks including spiral data tracks, as well as conventional concentric data tracks.
In an embodiment, there is a separation between the individual reader elements, which can vary greatly over process, for each head. For a TDMR data or servo operation, the separation of the reader elements is situated for optimal digital signal processing (DSP) of the signals from the different reader elements. In an embodiment, the reader element separation is measured with high precision at different locations on the disk (e.g., adjusting for different actuator positions). In an embodiment, the TDMR head increases the data density of the recording media. In an embodiment, two reader elements, while accessing a target track, are separated and offset from a position centerline of the target track. In an embodiment, when the second reader system, but not the first reader system, is caused to read the magnetic storage medium, then the second reader system head is repositioned to a position that is centerline to a target track.
FIG. 4 illustrates a reader failover method and process for a data storage device. It will be understood that each step in the flowchart illustration can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a programmable data processing apparatus, such that the instructions execute via the processor to implement the functions or actions specified in the flowchart. The instructions may be executed by a controller. In an embodiment, the controller is a component of a data storage device, such as a disk drive storage system. In an alternative embodiment, the controller is separate from the data storage device and may be connected to the data storage device to externally monitor and communicate with the data storage device.
In an embodiment, as detailed in step 402, at least two reader systems are employed to read a magnetic storage medium. The reader systems include a first reader system and a second reader system. The first reader system includes a first reader element, and the second reader system includes a second reader element. A first head includes both the first reader element and the second reader element.
Next, as stated in step 404, the method further includes detecting when the first reader system provides less than a predetermined performance or fails. Thereafter, the method includes causing the second reader system, but not the first reader system, to read the magnetic storage medium.
In an embodiment, before there is a detection that the first reader system provides less than a predetermined performance or fails, the first reader system and the second reader system are utilized together to read the magnetic storage medium. In an alternative embodiment, the second reader system is only employed in lieu of the first reader system, when the first reader system is determined to provide less than a predetermined performance or fails.
In an embodiment, the failover method and system includes directing components of a TDMR drive such as servo, data channel, and controller firmware in the event that a reader system provides less than a predetermined performance or fails. For example, a data storage device firmware may have a contingency code that is activated upon detection of a reader system failure. In an embodiment, pre-defined normal and failure mode parameters/configuration values (e.g. related to channel, servo, etc.) may be stored in a lookup table (e.g., stored in non-volatile memory). In an embodiment, the memory may also be a disk media, with parameters read off of the reserve tracks at drive power up and stored in the system DDR buffer memory during operation of the hard drive. If failure mode is initiated the appropriate table values are used. Once the failover method is employed, the properly performing reader element(s) are employed. In an embodiment, if a reader system is determined to provide less than a predetermined performance, it may be used for a limited purpose.
FIG. 5 shows an embodiment of a read channel 506, and control circuitry 508 that monitors the performance of reader elements 502 and 504 for a data storage device. Signals from the two reader elements 502 and 504 (marked reader 1 and reader 2) are acquired in parallel to decode user data. In this example, inputs from two reader elements on one head are shown in the reader array. In an alternative embodiment, more than two reader elements on one head may be utilized to read a magnetic storage medium, and signals from multiple reader elements may input to a read channel and control circuitry. In an embodiment, the head that includes reader elements 502 and 504 is a two-dimensional magnetic recording (TDMR) head.
Any suitable control circuitry may be employed to implement the methods described herein, such as any suitable integrated circuit or circuits. For example, the control circuitry may be implemented within a read channel integrated circuit, or in a component separate from the read channel, such as a disk controller, or certain operations described herein may be performed by a read channel and others by a disk controller. In an embodiment, the read channel and disk controller are implemented as separate integrated circuits, and in an alternative embodiment they are fabricated into a single integrated circuit or system on a chip (SOC). In addition, the control circuitry may include a suitable preamp circuit implemented as a separate integrated circuit, integrated into the read channel or disk controller circuit, or integrated into a SOC. In embodiment, the control circuitry includes suitable logic circuitry, such as state machine circuitry.
In an embodiment, the control circuitry or DSP includes a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the methods described herein. The instructions may be stored in any computer-readable medium. In an embodiment, they may be stored on a non-volatile semiconductor memory external to the microprocessor, or integrated with the microprocessor in a SOC. In another embodiment, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on.
Reader element 502 is a portion of reader system 1. Reader system 1 further includes analog front end 510a, first analog-to-digital converter 512a, multiplexer 514, buffer 516a, equalizer 518, and digital back end 520.
Reader element 504 is a portion of reader system 2. Reader system 2 further includes analog front end 510b, first analog-to-digital converter 512b, multiplexer 514, buffer 516b, equalizer 518, and digital back end 520.
In an embodiment, control circuitry 508 detects when the reader system 1 provides less than a predetermined performance or fails, and thereafter causes reader system 2, but not reader system 1, to read the magnetic storage medium. In an embodiment, the control circuitry includes a controller and/or firmware. In an embodiment, one or more reader quality metrics (e.g., SNR of a signal) are detected by the control circuitry 508. In an embodiment, in-line calibrations may detect that a read element provides less than a predetermined performance or fails, despite failed sectors not being detected. In an embodiment, control circuitry 508 sets the data storage device to a data recovery mode when the reader system 1 provides less than the predetermined performance or fails. An alert is generated when the data storage device is set to the data recovery mode, and reader system 2 is directed to recover data from the magnetic storage medium.
In an embodiment, the data storage device initially attempts to recover storage medium data via conventional error recovery methods, but when the conventional error recovery methods fail to fully recover data, the methods of an embodiment are utilized. Further, in an embodiment, when reader system 1 and reader system 2 are both determined to provide less than a predetermined performance, then the control circuitry determines which reader system provides the better quality signal, and the reader system providing the better quality signal is utilized to read the magnetic storage medium.
In an embodiment, when reader element 502 is determined to provide less than a predetermined performance or fails, the offset of reader element 504 during the signal acquisition by reader element 504 is governed by optimization before deployment, and/or by operational constraints (e.g., ability to obtain timing information).
In an embodiment, when a signal is created via reader element 502, the reader system 1 passes the reader element 502 signal from reader element 502 to a preamplifier, to analog front end 506a, to analog-to-digital converter 512a, to multiplexer 514, to buffer 516a, to equalizer 518, and to digital back end 520.
In an embodiment, when a signal is created via reader element 504, the reader system 2 passes the reader element 504 signal from reader element 504 to a preamplifier, to analog front end 506b, to analog-to-digital converter 512b, to multiplexer 514, to buffer 516b, to equalizer 518, and to digital back end 520.
In an embodiment, when a signal from reader element 502 is created, the reader system 1 passes the reader element signal 502 from the reader element 502 to read channel 506, and from read channel 506 to controller 508. When a signal from reader element 504 is created, the reader system 2 passes the reader element signal 504 from the reader element 504 to read channel 506, and from read channel 506 to controller 508.
In an embodiment, the multiple reader element signals on one head input to one read channel. In an alternative embodiment, the multiple reader element signals input to separate read channels. In yet another embodiment, the multiple reader element signal pathways utilize portions of the same read channel, as well as utilize separate circuitry.
In an embodiment, buffer 516a stores the signal from reader element 502 until the control circuitry 508 detects whether or not reader system 1 provides less than the predetermined performance or fails.
In an embodiment, multiplexer 514 routes outputs from analog-to-digital converters 512a and 512b, to buffers 516a and 516b, storing any signal with a buffer when a signal is determined to provide less than the predetermined performance.
In an embodiment, a signal from reader system 2 is not utilized by the data storage device until reader system 1 provides less than the predetermined performance or fails.
In an embodiment, when there is a detection by control circuitry 508 that the first reader system provides less than a predetermined performance or fails, all of, or a portion of, reader system 1 is not utilized to read the magnetic storage medium. For example, when only one portion of reader system 1 fails (e.g., analog-to-digital converter 512a), reader system 1 may continue to use the functioning portion of reader system 1, and alternatively use a portion of reader system 2 (e.g., analog-to-digital converter 512b) to read the magnetic storage medium.
Similarly, in an embodiment, when reader system 2 is caused to read the magnetic storage medium, reader system 2 may utilize one portion or more than one portion of reader system 2 to read the magnetic storage medium.
In an embodiment, a third reader element is included with the head that includes reader elements 502 and 504. When control circuitry 508 detects that the third reader system provides less than a predetermined performance or fails, reader system 2, but not reader system 1 or the third reader element (including, e.g., a third reader system) is caused to read the magnetic storage medium.
In an embodiment, the data storage device detects being situated in a predetermined environmental condition, and proactively causes the second reader system, but not the first reader system, to read the magnetic storage medium. This failover method may be executed upon a determination of a likely prospective or predicted reader system failure. In an example, reader element circuits may be situated differently on a wafer, and may have different behavior. Due to the specific usage and calibration for the head, the reader elements may react differently to temperature and humidity. In an embodiment, a reader element may be temporarily disabled due to a predetermined environmental condition, and activated again later when the data storage device is not situated in the predetermined environmental condition.
Embodiments may be used in lieu of full reconstruction in redundant array of independent disks (RAID), thereby reducing the bandwidth and time required for data recovery.
Turning now to FIG. 6, components of system 600 are illustrated, in an embodiment. System 600 includes processor module 604, storage module 606, input/output (I/O) module 608, memory module 610, and bus 602. Although system 600 is illustrated with these modules, other suitable arrangements (e.g., having more or less modules) known to those of ordinary skill in the art may be used. For example, system 600 may be a logic implemented state machine or a programmable logic controller.
In an embodiment, the methods described herein are executed by system 600. Specifically, processor module 604 executes one or more sequences of instructions contained in memory module 610 and/or storage module 606. In one example, instructions may be read into memory module 610 from another machine-readable medium, such as storage module 606. In another example, instructions may be read directly into memory module 610 from I/O module 608, for example from an operator via a user interface. Information may be communicated from processor module 604 to memory module 610 and/or storage module 606 via bus 602 for storage. In an example, the information may be communicated from processor module 304, memory module 610, and/or storage module 606 to I/O module 608 via bus 602. The information may then be communicated from I/O module 608 to an operator via the user interface.
Memory module 610 may be random access memory or other dynamic storage device for storing information and instructions to be executed by processor module 604. In an example, memory module 610 and storage module 606 are both a machine-readable medium.
In an embodiment, processor module 604 includes one or more processors in a multi-processing arrangement, where each processor may perform different functions or execute different instructions and/or processes contained in memory module 610 and/or storage module 606. For example, one or more processors may execute instructions for detecting read element performance, and one or more processors may execute instructions for input/output functions. Also, hard-wired circuitry may be used in place of or in combination with software instructions to implement various example embodiments. Thus, embodiments are not limited to any specific combination of hardware circuitry and software.
The term “circuit” or “circuitry” as used herein includes all levels of available integration, for example, from discrete logic circuits to the highest level of circuit integration such as VLSI, and includes programmable logic components programmed to perform the functions of embodiments as well as general-purpose or special-purpose processors programmed with instructions to perform those functions.
Bus 602 may be any suitable communication mechanism for communicating information. Processor module 604, storage module 606, I/O module 608, and memory module 610 are coupled with bus 602 for communicating information between any of the modules of system 600 and/or information between any module of system 600 and a device external to system 600. For example, information communicated between any of the modules of system 600 may include instructions and/or data.
The term “machine-readable medium” as used herein, refers to any medium that participates in providing instructions to processor module 304 for execution. Such a medium may take many forms, including, but not limited to, non-volatile media, and volatile media. Non-volatile media includes, for example, optical or magnetic disks, such as storage module 306. Volatile media includes dynamic memory, such as memory module 310. Common forms of machine-readable media or computer-readable media include, for example, floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical mediums with patterns of holes, a RAM, a PROM, an EPROM, a FLASH EPROM, any other memory chip or cartridge, or any other medium from which a processor can read.
In an embodiment, a non-transitory machine-readable medium is employed including executable instructions for a data storage device. The instructions include code for detecting when a first reader system provides less than a predetermined performance or fails, and thereafter causing a second reader system, but not the first reader system, to read the magnetic storage medium. In this embodiment, the data storage device employs at least two reader systems to read the magnetic storage medium. The at least two reader systems include the first reader system and the second reader system, wherein the first reader system includes a first reader element, and the second reader system includes a second reader element. A first head includes both the first reader element and the second reader element. In an embodiment, the first head is a two-dimensional magnetic recording (TDMR) head.
In an embodiment, the non-transitory machine-readable medium further includes executable instructions for storing the first reader element signal until detecting whether or not the first reader system provides less than the predetermined performance or fails.
In an embodiment, the non-transitory machine-readable medium further includes executable instructions for setting the data storage device to a data recovery mode when the first reader system provides less than a predetermined performance or fails; providing an alert when the data storage device is set to a data recovery mode; and utilizing the second reader system to recover data.
The various features and processes described herein may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure. In addition, certain method, event or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described tasks or events may be performed in an order other than that specifically disclosed, or multiple may be combined in a single block or state. The example tasks or events may be performed in serial, in parallel, or in some other manner. Tasks or events may be added to or removed from the disclosed example embodiments. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example embodiments.
While certain example embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the embodiments disclosed herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the embodiments disclosed herein.
Modifications and variations may be made to the disclosed embodiments while remaining within the spirit and scope of the methods, systems and apparatus. The implementations described above and other implementations are within the scope of the following claims.

## Claims

1. An apparatus for a data storage device comprising:
at least a first reader system and a second reader system to read a magnetic storage medium, wherein the first reader system includes a first reader element, and the second reader system includes a second reader element, and wherein a first head includes both the first reader element and the second reader element;
control circuitry to detect when the first reader system provides less than a predetermined performance or fails, and thereafter to cause the second reader system, but not the first reader system, to read the magnetic storage medium; and
the control circuitry to further detect when a third reader system provides less than the predetermined performance or is nonfunctioning, and thereafter to cause the second reader system, but not the third reader system, to read the magnetic storage medium, wherein the third reader system includes a third reader element, and wherein the first head further includes the third reader element.

2. The apparatus of claim 1, wherein the first head is a two-dimensional magnetic recording (TDMR) head.

3. The apparatus of claim 1, wherein the control circuitry:
sets the data storage device to a data recovery mode when the first reader system provides less than the predetermined performance or fails;
provides an alert when the data storage device is set to the data recovery mode; and
directs the second reader system to recover data from the magnetic storage medium.

4. The apparatus of claim 1, wherein:
when a first reader element signal is created, the first reader system passes the first reader element signal from the first reader element to a first read channel, and from the first read channel to the control circuitry; and
when a second reader element signal is created, the second reader system passes the second reader element signal from the second reader element to a second read channel, and from the second read channel to the control circuitry.

5. The apparatus of claim 1, wherein when a first reader element signal is created, the first reader system passes the first reader element signal from the first reader element to a first preamplifier, to a first analog front end, to a first analog-to-digital converter, to a multiplexer, to a first buffer, to an equalizer, and to a digital back end;
wherein a first read channel includes the first analog front end, the first analog-to-digital converter, the multiplexer, the first buffer, the equalizer, and the digital back end;
wherein when a second reader element signal is created, the second reader system passes the second reader element signal from the second reader element to a second preamplifier, to a second analog front end, to a second analog-to-digital converter, to the multiplexer, to a second buffer, to the equalizer, and to the digital back end; and
wherein a second read channel includes the second analog front end, the second analog-to-digital converter, the multiplexer, the second buffer, the equalizer, and the digital back end.

6. The apparatus of claim 5, wherein the first buffer stores the first reader element signal until the control circuitry detects whether or not the first reader system provides less than the predetermined performance or fails.

7. A method for a data storage device, comprising:
employing at least a first reader system and a second reader system to read a magnetic storage medium, wherein the first reader system includes a first reader element, and the second reader system includes a second reader element, and wherein a first head includes both the first reader element and the second reader element;
detecting when the first reader system provides less than a predetermined performance or fails, and thereafter causing the second reader system, but not the first reader system, to read the magnetic storage medium; and
detecting when a third reader system provides less than the predetermined performance or is nonfunctioning, and thereafter causing the second reader system, but not the third reader system, to read the magnetic storage medium, wherein the third reader system includes a third reader element, and wherein the first head further includes the third reader element.

8. The method of claim 7, further comprising not utilizing a signal from the second reader system by the data storage device until the first reader system provides less than the predetermined performance or fails.

9. The method of claim 7, wherein the first head is a two-dimensional magnetic recording (TDMR) head.

10. The method of claim 7, wherein:
causing the second reader system to read the magnetic storage medium comprises utilizing one portion or more than one portion of the second reader system to read the magnetic storage medium; and
causing the first reader system to not read the magnetic storage medium comprises not utilizing one portion or more than one portion of the first reader system.

11. The method of claim 7, further comprising utilizing a controller to detect when the first reader system provides less than the predetermined performance or fails, and thereafter to cause the second reader system, but not the first reader system, to read the magnetic storage medium.

12. The method of claim 11, wherein:
when a first reader element signal is created, the first reader system passes the first reader element signal from the first reader element to a first read channel, and from the first read channel to the controller; and
when a second reader element signal is created, the second reader system passes the second reader element signal from the second reader element to a second read channel, and from the second read channel to the controller.

13. The method of claim 11, further comprising storing the first reader element signal, utilizing a buffer, until the controller detects whether or not the first reader system provides less than the predetermined performance or fails.

14. The method of claim 7, further comprising setting the data storage device to a data recovery mode when the first reader system provides less than a predetermined performance or fails, providing an alert when the data storage device is set to a data recovery mode, and utilizing the second reader system to recover data.

15. The method of claim 7, further comprising:
detecting that the data storage device is situated in a predetermined environmental condition; and
causing the second reader system, but not the first reader system, to read the magnetic storage medium.

16. A non-transitory machine-readable medium including executable instructions for a data storage device, the instructions comprising code for:
employing at least a first reader system and a second reader system to read a magnetic storage medium, wherein the first reader system includes a first reader element, and the second reader system includes a second reader element, and wherein a first head includes both the first reader element and the second reader element;
detecting when the first reader system provides less than a predetermined performance or fails, and thereafter causing the second reader system, but not the first reader system, to read the magnetic storage medium; and
detecting when a third reader system provides less than the predetermined performance or is nonfunctioning, and thereafter causing the second reader system, but not the third reader system, to read the magnetic storage medium, wherein the third reader system includes a third reader element, and wherein the first head further includes the third reader element.

17. The non-transitory machine-readable medium of claim 16, wherein the first head is a two-dimensional magnetic recording (TDMR) head.

18. The non-transitory machine-readable medium of claim 16, further comprising storing the first reader element signal until detecting whether or not the first reader system provides less than the predetermined performance or fails.

19. The non-transitory machine-readable medium of claim 16, further comprising setting the data storage device to a data recovery mode when the first reader system provides less than a predetermined performance or fails, providing an alert when the data storage device is set to a data recovery mode, and utilizing the second reader system to recover data.

20. A method for a data storage device, comprising:
employing at least two reader systems to read a magnetic storage medium, wherein the at least two reader systems include a first reader system and a second reader system, wherein the first reader system includes a first reader element, and the second reader system includes a second reader element, and wherein a first head includes both the first reader element and the second reader element; and
detecting when the first reader system provides less than a predetermined performance or fails, due to a factor that is independent from concurrent use of the first reader system and the second reader system, and thereafter causing the second reader system, but not the first reader system, to read the magnetic storage medium.

21. The method of claim 20, further comprising setting the data storage device to a data recovery mode when the first reader system provides less than a predetermined performance or fails, providing an alert when the data storage device is set to a data recovery mode, and utilizing the second reader system to recover data.

22. The method of claim 20, further comprising determining whether a portion of the first reader system provides less than a predetermined performance or fails, and utilizing a functioning portion of the first reader system.