Patent Publication Number: US-2023141431-A1

Title: Hybrid Dedicated and Dynamic Servo for Tape

Description:
BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     Embodiments of the present disclosure generally relate to a tape head and a tape drive including a tape head. 
     Description of the Related Art 
     Tape heads of tape drive systems are used to record and read back information on tapes by magnetic processes. Magnetic transducers of the tape heads read data from and write data onto magnetic recording media. Data is written on the magnetic recording media by moving a magnetic write transducer to a location over the media where the data is to be stored. The magnetic write transducer then generates a magnetic field, which encodes the data into the magnetic media. Data is read from the media by the magnetic read transducer through sensing of the magnetic field of the magnetic media. 
     To position the tape head accurately when reading from and writing to a magnetic tape, servo heads are used to read servo positioning information from servo tracks on the tape. The servo tracks comprising the positioning information are written to the tape once, at the media factory, at the beginning of the life of the tape. However, tapes may stretch and/or compress both in tape length and width over time due to a variety of reasons, such as environmental causes like humidity and temperature, workload, and general wear of the tape. As such, as the tape stretches and compresses, the positioning information in the servo tracks may become outdated, thus making accurate positioning of the tape head difficult. 
     Therefore, there is a need in the art for a tape head capable of accurate positioning over a tape dynamically. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure generally relates to a tape head and a tape drive including a tape head. The tape head comprises servo heads configured to read servo data from a tape, a plurality of write heads configured to: write user data to a plurality of data tracks of the tape and write embedded servo data into one or more data fields of the tape, the embedded servo data comprising servo positioning information, and a plurality of read heads configured to read the user data and the embedded servo data from the tape. The embedded servo data may be embedded servo fields or embedded servo tracks. The embedded servo data allows the tape head to be accurately controlled and positioned above the tape, and for new data to be accurately appended to the tape. 
     In one embodiment, a tape head assembly comprises one or more servo heads configured to read servo data from one or more dedicated servo tracks of a tape, a plurality of write heads configured to: write user data to a plurality of data tracks of the tape and write one or more embedded servo fields into one or more data fields of the plurality of data tracks of the tape, the one or more embedded servo fields comprising servo positioning information, and a plurality of read heads configured to read the user data and the embedded servo fields from the tape. 
     In another embodiment, a tape head assembly comprises one or more servo heads configured to read servo data from one or more dedicated servo tracks of a tape, a plurality of write heads configured to: write user data to a plurality of data tracks of the tape and write one or more embedded servo tracks into one or more data tracks of the tape, the one or more embedded servo tracks comprising servo positioning information, wherein the plurality of data tracks and the one or more embedded servo tracks have a same length, and wherein the one or more embedded servo fields are erasable and re-writeable, and a plurality of read heads configured to read the user data and the embedded servo fields from the tape. 
     In yet another embodiment, a tape drive comprises a tape head assembly comprising: one or more servo heads configured to read servo data from one or more dedicated servo tracks of a tape, a plurality of write heads configured to: write user data to a plurality of data tracks of the tape and write embedded servo positioning information into one or more data fields of the plurality of data tracks of the tape, and a plurality of read heads configured to read the user data and the embedded servo positioning information from the tape. The tape drive further comprises a controller coupled to the tape head assembly, the controller configured to: dynamically tilt the tape head assembly based on the read embedded servo positioning information, and determine where to append new data to the plurality of data tracks based on the read embedded servo positioning information. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
         FIGS.  1 A- 1 C  illustrate a perspective exploded view, a simplified top down, and side profile view of a tape drive, in accordance with some embodiments. 
         FIG.  2    is a schematic illustration of a tape head and tape that are aligned. 
         FIG.  3 A  illustrates a conventional magnetic tape comprising a first dedicated servo track, a second dedicated servo track, and a plurality of data tracks, according to one embodiment. 
         FIGS.  3 B- 3 E  illustrate a magnetic tape comprising embedded servo fields in addition to a first dedicated servo track, a dedicated second servo track, and a plurality of data tracks, according to one embodiment. 
         FIGS.  4 A- 4 B  illustrate magnetic tapes comprising dedicated servo tracks and a plurality of data tracks, according to various embodiments. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
     In the following, reference is made to embodiments of the disclosure. However, it should be understood that the disclosure is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the disclosure. Furthermore, although embodiments of the disclosure may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the disclosure. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the disclosure” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s). 
     The present disclosure generally relates to a tape head and a tape drive including a tape head. The tape head comprises servo heads configured to read servo data from a tape, a plurality of write heads configured to: write user data to a plurality of data tracks of the tape and write embedded servo data into one or more data fields of the tape, the embedded servo data comprising servo positioning information, and a plurality of read heads configured to read the user data and the embedded servo data from the tape. The embedded servo data may be embedded servo fields or embedded servo tracks. The embedded servo data allows the tape head to be accurately controlled and positioned above the tape, and for new data to be accurately appended to the tape. 
       FIGS.  1 A- 1 C  illustrate a perspective exploded view, a simplified top down, and side profile view of a tape drive  100 , in accordance with some embodiments. The tape drive  100  may be a tape embedded drive (TED). Focusing on  FIG.  1 B , for example, the tape drive comprises a casing  105 , one or more tape reels  110 , one or more motors (e.g., a stepping motor  120  (also known as a stepper motor), a voice coil motor (VCM)  125 , etc.), a head assembly  130  with one or more read heads and one or more write heads, and tape guides/rollers  135   a ,  135   b , and a controller  140  coupled to the head assembly  130 . In the descriptions herein, the term “head assembly” may be referred to as “magnetic recording head”, interchangeably, for exemplary purposes. Focusing on  FIG.  1 C , for example, the tape drive further comprises a printed circuit board assembly (PCBA)  155 . In an embodiment, most of the components are within an interior cavity of the casing, except the PCBA  155 , which is mounted on an external surface of the casing  105 . The same components are illustrated in a perspective view in  FIG.  1 A . In the descriptions herein, the term “tape” may be referred to as “magnetic media”, interchangeably, for exemplary purposes. 
     In the illustrated embodiments, two tape reels  110  are placed in the interior cavity of the casing  105 , with the center of the two tape reels  110  on the same level in the cavity and with the head assembly  130  located in the middle and below the two tape reels  110 . Tape reel motors located in the spindles of the tape reels  110  can operate to wind and unwind the tape media  115  in the tape reels  110 . One or more of the tape reels  110  may form a part of a removable cartridge and are not necessarily part of the tape drive  100 . In such embodiments, the tape drive  100  may not be a tape embedded drive as it does not have embedded media, the drive  100  may instead be a tape drive configured to accept and access magnetic media or tape media  115  from an insertable cassette or cartridge (e.g., an LTO drive), where the insertable cassette or cartridge further comprises one or more of the tape reels  110  as well. In such embodiments, the tape or media  115  is contained in a cartridge that is removable from the drive  100 . 
     The tape media  115  comprises a base film, which can be PEN, PET, aramid or any similar plastic material, a magnetic recording layer on the front side of the tape media, and a back coat. The magnetic recording layer can be particulate in nature (e.g., barium ferrite or strontium ferrite particles, or metal particles), or fabricated using thin film sputtering techniques. The magnetic recording layer is the surface that can be magnetically manipulated (written to or read from) by one or more read/write heads. The back coat is applied to the reverse side of the base film to improve the mechanical characteristics of the tape media and aid in packing the tape  115  onto the tape reels and guide the tape  115  through the tape path components. 
     Tape media  115  from the tape reels  110  are biased against the guides/rollers  135   a ,  135   b  (collectively referred to as guides/rollers 135) and are movably passed along the head assembly  130  by movement of the reels  110 . The illustrated embodiment shows four guides/rollers  135   a ,  135   b , with the two guides/rollers  135   a  furthest away from the head assembly  130  serving to change direction of the tape media  115  and the two guides/rollers  135   b  closest to the head assembly  130  by pressing the tape media  115  against the head assembly  130 . As shown in  FIG.  1 A , in some embodiments, the guides/rollers  135  utilize the same structure. In other embodiments, as shown in  FIG.  1 B , the guides/rollers  135  may have more specialized shapes and differ from each other based on function. Furthermore, a lesser or a greater number of rollers may be used. 
     The voice coil motor  125  and stepping motor  120  may variably position the tape head(s) transversely with respect to the width of the recording tape. The stepping motor  120  may provide coarse movement, while the voice coil motor  125  may provide finer actuation of the head(s). In an embodiment, servo data may be written to the tape media to aid in more accurate position of the head(s) along the tape media  115 . 
     In addition, the casing  105  comprises one or more particle filters  141  and/or desiccants  142 , as illustrated in  FIG.  1 A , to help maintain the environment in the casing. For example, if the casing is not airtight, the particle filters may be placed where airflow is expected. The particle filters and/or desiccants may be placed in one or more of the corners or any other convenient place away from the moving internal components. For example, the moving reels may generate internal airflow as the tape media winds/unwinds, and the particle filters may be placed within that airflow. 
     There is a wide variety of possible placements of the internal components of the tape drive  100  within the casing  105 . In particular, as the head mechanism is internal to the casing in certain embodiments, the tape media  115  may not be exposed to the outside of the casing  105 , such as in conventional tape drives. Thus, the tape media  115  does not need to be routed along the edge of the casing  105  and can be freely routed in more compact and/or otherwise more efficient ways within the casing  105 . Similarly, the head(s)  130  and tape reels  110  may be placed in a variety of locations to achieve a more efficient layout, as there are no design requirements to provide external access to these components. 
     As illustrated in  FIG.  1 C , the casing  105  comprises a cover  150  and a base  145 . The PCBA  155  is attached to the bottom, on an external surface of the casing  105 , opposite the cover  150 . As the PCBA  155  is made of solid state electronics, environmental issues are less of a concern, so it does not need to be placed inside the casing  105 . That leaves room inside casing  105  for other components, particularly, the moving components and the tape media  115  that would benefit from a more protected environment. 
     In some embodiments, the tape drive  100  is sealed. Sealing can mean the drive is hermetically sealed or simply enclosed without necessarily being airtight. Sealing the drive may be beneficial for tape film winding stability, tape film reliability, and tape head reliability. Desiccant may be used to limit humidity inside the casing  105 . 
     In one embodiment, the cover  150  is used to hermetically seal the tape drive. For example, the drive  100  may be hermetically sealed for environmental control by attaching (e.g., laser welding, adhesive, etc.) the cover  150  to the base  145 . The drive  100  may be filled by helium, nitrogen, hydrogen, or any other typically inert gas. 
     In some embodiments, other components may be added to the tape drive  100 . For example, a pre-amp for the heads may be added to the tape drive. The pre-amp may be located on the PCBA  155 , in the head assembly  130 , or in another location. In general, placing the pre-amp closer to the heads may have a greater effect on the read and write signals in terms of signal-to-noise ratio (SNR). In other embodiments, some of the components may be removed. For example, the filters  141  and/or the desiccant  142  may be left out. 
     In various embodiments, the drive  100  includes controller integrated circuits (IC) (or more simply “a controller”) (e.g., in the form of one or more System on Chip (SoC)), along with other digital and/or analog control circuitry to control the operations of the drive. For example, the controller and other associated control circuitry may control the writing and reading of data to and from the magnetic media, including processing of read/write data signals and any servo-mechanical control of the media and head module. In the description below, various examples related to writing and reading and verifying of written data, as well as control of the tape head and media to achieve the same, may be controlled by the controller. As an example, the controller may be configured to execute firmware instructions for the various same gap verify embodiments described below. 
       FIG.  2    is a schematic illustration of a tape head module assembly  200  and a tape  204  that are aligned. The tape head module assembly  200  comprises a tape head body  202  that is aligned with the tape  204 . The tape  204  moves past the tape head module assembly  200  during read and/or write operations. The tape head module assembly  200  has a media facing surface (MFS)  214  that faces the tape  204 . The tape head module assembly  200  is coupled to a controller  240 . 
     The tape head body  202  comprises a first servo head  206 A and a second servo head  206 B spaced therefrom. It is to be understood that while two servo heads have been shown, the disclosure is not limited to two servo heads. Rather, it is contemplated that more or less servo heads may be present. A plurality of data heads  208 A- 208 G is disposed between the first servo head  206 A and the second servo head  206 B. It is to be understood that while seven data heads have been shown, the disclosure is not limited to seven data heads. Rather, the number of data heads can be more or less than seven, depending on the requirements of the embodiment. For example there can be sixteen, thirty two, sixty four or more data heads utilized in the tape head body  202 . 
     A plurality of pads  220 A- 220 N is electrically coupled to the data head body  202 . The plurality of pads  220 A- 220 N coupled to the data head body  202  is not limited to the number shown in  FIG.  2   . Rather, more or less pads are contemplated. The pads  220 A- 220 N are used to connect the drive electronics to the servo heads  206 A,  206 B and to data read and writer elements. The pads  220 A- 220 N are used to establish the electrical potential across the servo reader by means of a power supply (not shown) embedded in the tape head  200 . 
     The tape  204  comprises a first servo track  210 A and a second servo track  210 B. The first servo track  210 A and the second servo track  210 B are spaced apart allowing the tape head  200  to monitor and control the average position of the data heads  208 A- 208 G relative to the data tracks  212 A- 212 G on the tape  204 . It is to be understood that while two servo tracks have been shown, the disclosure is not limited to two servo tracks. Rather, the number of servo tracks can be more or less than two, depending on the requirements of the embodiment. 
     The tape  204  further comprises a plurality of data tracks  212 A- 212 G disposed between the first servo track  210 A and the second servo track  210 B. It is to be understood that while seven data tracks have been shown, the disclosure is not limited to the seven data tracks. Rather, the number of data tracks can be more or less than seven, depending on the requirements of the embodiment. In the embodiment of  FIG.  2   , the first servo head  206 A reads its lateral position information (e.g., alignment) over the first servo track  210 A. The second servo head  206 B is aligned with the second servo track  210 B. The combined information allows the servo actuator of the tape drive  200  to align the data heads  208 A- 208 G such that the center data track (e.g.,  208 D) is centered on tape  204 . The plurality of data heads  208 A- 208 G is thus individually aligned with the plurality of data tracks  212 A- 212 N for best case positioning. In this embodiment the first servo head  206 A, the second servo head  206 B, the first servo track  210 A, the second servo track  210 B, the plurality of data heads  208 A- 208 G, and the plurality of data tracks  212 A- 212 G are able to read and/or write the data accurately because all are aligned perpendicular to the direction of travel of the tape  204 . 
       FIGS.  3 A- 3 E  illustrate magnetic tapes  300 ,  350  comprising dedicated servo tracks  302   a ,  302   b  and a plurality of data tracks  304 . Each of the magnetic tapes  300 ,  350  may be the tape  204  of  FIG.  2   , and may be utilized with a tape head module assembly, such as the tape head module assembly  200  of  FIG.  2   , or a tape drive, such as the tape drive  100  of  FIG.  1   . As such, aspects of  FIG.  2    may be referred to in the description of  FIGS.  3 A- 3 E . 
     While not shown, a plurality of write heads of a tape assembly as configured to write user data and embedded servo fields from the tape, a plurality of read heads of the tape assembly are configured to read user data and embedded servo fields from the tape, and one or more servo heads of a tape head assembly are configured to read the dedicated servo tracks from the tape. The tape head assembly is coupled to a controller (not shown) of a tape drive (not shown). 
     Each tape  300 ,  350  comprises one or more dedicated servo tracks  302   a ,  302   b . The dedicated servo tracks  302   a ,  302   b  may collectively be referred to herein as servo tracks  302 . It is to be understood that while two servo tracks  302   a ,  302   b  are shown in each of  FIGS.  3 A- 3 E , the disclosure is not limited to two servo tracks  302 . Rather, the number of servo tracks  302  can be more or less than two, depending on the requirements of the embodiment. Similarly, the number of data tracks  304  is not intended to be limiting, and a greater or fewer number of data tracks  304  than shown may be used. 
       FIG.  3 A  illustrates a conventional magnetic tape  300  comprising a first dedicated servo track  302   a , a second dedicated servo track  302   b , and a plurality of data tracks  304 , according to one embodiment. The first servo track  302   a  and the second servo track  302   b  are spaced apart in the y-direction by the plurality of data tracks  304  to allow a tape head  200  to monitor and control the average position of the data heads  208 A- 208 G relative to the data tracks  304  on the tape  300 . Positioning information for servo heads  206 A,  206 B to read is written to each servo track  302   a ,  302   b  once, at the media factory, at the beginning of the life of the tape  300 . With conventional tapes  300 , the servo information is written only the one time at the factory, and new servo information is not written at a later time. 
       FIG.  3 B  illustrates a magnetic tape  350  comprising embedded servo fields  306   a ,  306   b  in addition to the first dedicated servo track  302   a , the dedicated second servo track  302   b , and the plurality of data tracks  304 , according to one embodiment. The embedded servo fields  306   a ,  306   b  may be collectively referred to herein as embedded servo fields  306 . 
     The embedded servo fields  306  comprise servo positioning information written into one or more data fields of the tape  350  when user data is being written to the tape  350 . When the tape  350  moves in a first direction  310   a  (e.g., the x-direction), first embedded servo fields  306   a  are written to a first or upper portion  330   a  of the tape  350 . When the tape  350  moves in a second direction  310   b  opposite the first direction  310  (e.g., the -x-direction), second embedded servo fields  306   b  are written to a second or lower portion  330   b  of the tape  350 . 
     The embedded servo fields  306  may be written into one or more of data fields of the data channels or tracks  304  simultaneously as user data is being written to the data tracks  304 . The embedded servo fields  306  are inserted periodically along the length of the tape  350 . The embedded servo fields  306  may have a consistent or asymmetric distribution along the length of the tape  350 . A controller of a tape head (not shown) may receive and analyze the positioning information read from the embedded servo fields  306 . 
     The positioning information stored in the embedded servo fields  306  may include information of one or more parameters: servo busts, servo phase locked loop (PLL), environmental measurements, environmental sensor information, such as from temperature or humidity sensors, position error signals, workload or wear counters, tape tension, friction, and tilt angle, among others. The positioning information and various parameters written in the embedded servo fields  306  may be used to accurately append data to the data tracks  304 . 
     With respect to measured servo bursts, upon read-back of the tape  350 , the servo tracks  302  are used to locate the starting position targeted for read, as well as to maintain a position error signal (PES) and to compute a tape dimensional stability (TDS) offset by determining how the servo tracks  302  are spaced given any contraction or expansion. PES is the calculated error based from the dedicated servo tracks  302  and the recently read embedded servo fields  306 . In addition to the positioning information stored in the servo tracks  302 , the embedded servo fields  306  process interrupted measured embedded servo A-B-C-D bursts, help calculate a TDS offset, such as by comparing PES information from the dedicated servo tracks  302  to the embedded servo fields  306 , and apply the TDS offset to the PES, which would in turn be applied to the VCM. The TDS offset compensation tracks TDS changes of both narrowing and widening in the Y-axis (narrow width) of the tape  350 . 
     With respect to servo PLL, a known frequency PLL is added in the embedded servo fields  306  written to the data channels that can be measured and processed (i.e., servo PLL). The known frequency PLL enables channel frequency tuning, on a per channel basis. The servo PLL would provide information to calculate TDS information, such as whether the tape  350  was stretched (where the tape  350  would be read back at lower frequency) or compressed (where the tape  350  would be read back at higher frequency), and potentially adjust the data channel along the length (e.g., the x-direction). 
     With respect to environmental measurements, it is well known that humidity and temperature changes effect TDS of a tape  350  over time. Writing the embedded servo fields  306  including such environmental measurements at the time of write provides a path to characterize and calibrate TDS over the environmental changes. For example, if the tape  350  is written under hot and wet conditions, and a TDS characterization indicates the hot and wet writing conditions, the tape drive  100  may calibrate read-back or read-back error recoveries. 
     With respect to workload and wear counters, some areas of the tape  350  may have a different workload than others, such as in a banded or zoned tape format. Workload and wear are two attributes which affect TDS. Characterizing such workload and wear attributes in the embedded servo fields  306  enables the workload and wear attributes to be applied to read-back error recoveries. 
     The embedded servo fields  306  enhance positioning of the tape head  200  when used with the servo tracks  302 . Because the embedded servo fields  306  are written when the tape  350  is written with user data, the embedded servo fields  306  contain reference data describing the state of the tape  350  at the time the data is written to the tape  350  in both the x- and y-directions of the tape  350 , for example, any stretching and/or compression of both the length and width of the tape  350  which may have occurred while data was being written or read, or while the tape  350  was not in use (e.g., stored for a period of time). 
     For example, the dedicated servo tracks  302  may first be read-back to determine the expected conditions of the tape  350  and where the data is expected to be, and then the embedded servo fields  306  may be read-back to determine the actual conditions of the tape  350  and where the data actually is. By comparing the information read from the dedicated servo tracks  302  to the information read from the embedded servo fields  306 , new data may be accurately appended to previously written data on the tape. Furthermore, the embedded servo fields  306  may be erased and re-written as user data is erased and re-written from the tape  350 . For example, first TDS information may be written to the embedded servo fields  306  a first time. The embedded servo fields  306  may then be erased at some point, and second TDS information may be written to the embedded servo fields  306  at a second time. The first and second TDS information may be different based on the state of the tape  350  at the first time and at the second time. In other words, the second TDS information may be updated TDS information. 
       FIGS.  3 C- 3 E  illustrate exemplary embodiments of utilizing the embedded servo fields  306  to determine non-linear effects on the tracks per inch (TPI) of data written to a tape  350 , according to various embodiments. A head assembly  320  comprises a plurality of read transducers  322  and a plurality of write transducers (not shown) is configured to read data from the tape  350 . The head assembly  320  may be the tape head module assembly  200  of  FIG.  2   , and the read transducers  322  may be the data heads  208 A- 208 G of  FIG.  2   . In each of  FIGS.  3 C- 3 E , the tape  350  comprises the dedicated servo tracks  302 , a plurality of embedded servo fields  306 , and a plurality of data tracks  304 . While four embedded servo fields  306  are shown, any number of embedded servo fields  306  may be utilized, as described above. As such, the number of embedded servo fields  306  is not intended to be limiting. Similarly, the number of data tracks  304  shown is not intended to be limiting either. 
     When writing data and embedded servo information to the tape  350 , the head assembly  320  was un-tilted (e.g., aligned with the y-axis), like shown in  FIG.  3 C . After a period of time, the tape  350  may be read and found to have changed or become deformed. For instance, the tape  350  is shown to be compressed in some areas (arrows  324 ) and expanded in other areas (arrows  326 ) due to various factors or parameters, such as environmental factors or workload and wear factors, for example. Towards the beginning of the tape  350  (BOT), the tape  350  is shown to be expanded  326  on the outer edges disposed closest to the servo tracks  302  and compressed  324  towards the center of the tape  350 . Towards the end of the tape  350  (EOT), the tape  350  is shown to be compressed  324  on the outer edges disposed closest to the servo tracks  302  and expanded  326  towards the center of the tape  350 . However, the compression and the expansion shown in  FIGS.  3 C- 3 E  is for exemplary purposes only and is not intended to be limiting in any way. As such, the embedded servo fields  306  may be utilized with a tape  350  that is only compressed, only expanded, a combination of both compressed and expanded, or neither compressed nor expanded. Furthermore, the compression and the expansion shown in  FIGS.  3 C- 3 E  is shown to be in the x-direction, but the tape  350  may also expand and/or compress in the y-direction and the -y-direction as well. 
     In order to read data from data tracks  304  that have been compressed or expanded, the head assembly  320  may need to be dynamically tilted by a controller (not shown) of a tape drive comprising the head assembly  320 . By reading the embedded servo fields  306  upon discovering the state of the tape  350 , an optimal tilt angle for the head assembly  320  can be determined to read the data from the data tracks  304 . For example, the data may first be read back when the head assembly  320  is un-tilted. While some data may be readable, other data may not be. The embedded servo fields  306  may provide information regarding the state of the data on the tape  350 , which would be used to find the optimal tilt angle for the head assembly  320  to be able to read all of the data. 
     As shown in the embodiment of  FIG.  3 D , the head assembly is tilted in a first direction, such as in the -xy-direction. Tilting the head assembly  320  in the first direction may enable additional data to be readable, such as the data written in the expanded portions  326  of the tape  350 . As shown in the embodiment of  FIG.  3 E , the head assembly may be titled in a second direction different than the first direction, such as in the xy-direction. Tilting the head assembly  320  in the second direction may enable further data to be readable, such as the data written in the compressed portions  324  of the tape  350 . Upon reading the data after tilting the head assembly  320 , the various tilt angles of the head assembly  320  may be written in the embedded servo fields  306  when appending data to the tape  350 . 
     The tilting of  FIGS.  3 D- 3 E  in either direction from the y-direction has exactly the same effect, in that the longitudinal span between the outer data tracks  304  and embedded servo fields  306  (i.e., closer to the BOT or EOT) is reduced in a transverse direction. The titling in both directions isn’t necessary, but rather, may be tilted like shown in either  FIG.  3 D  or  FIG.  3 E . The data tracks  304  and embedded servo fields  306  would be initially written at some nominal tilt angle from the y-direction (thereby setting the span between the outer written data tracks  304  and embedded servo fields  306  on tape  350 ). If the tape  350  expands, then the data is read by decreasing the tilt angle relative to the writing angle. If the tape shrinks, then the head  320  is tilted further to line up the readers with the (now reduced pitch) of the written data tracks  304  and embedded servo fields  306 . The tilt angle is thus only set to one angle when writing and then set to second angle (which is determined by the expansion or contraction of the tape  350 ) when reading. 
       FIGS.  4 A- 4 B  illustrate magnetic tapes  400 ,  450  comprising dedicated servo tracks  302   a ,  302   b  and a plurality of data tracks  304 . Each magnetic tape  400 ,  450  may be the tape  204  of  FIG.  2   , and may be utilized with a tape head module assembly, such as the tape head module assembly  200  of  FIG.  2   , or a tape drive, such as the tape drive  100  of  FIG.  1   . While not shown, a plurality of write heads of a tape assembly as configured to write user data and embedded servo fields from the tape, a plurality of read heads of the tape assembly are configured to read user data and embedded servo fields from the tape, and one or more servo heads of a tape head assembly are configured to read the dedicated servo tracks from the tape. The tape head assembly is coupled to a controller (not shown) of a tape drive (not shown). 
     The tape  400  is similar to the tape  350  of  FIGS.  3 B- 3 D ; however the tape  400  comprises an embedded servo track  406 , which is written at the same time the data tracks  304  are written, rather than the embedded servo fields  306 . In some embodiments, the tape  400  may also comprise the one or more embedded servo fields  306  of  FIGS.  3 B- 3 D  in addition to the embedded servo track  406 . The embedded servo track  406  comprises servo positioning information written into one or more data tracks  304  of the tape  400  when user data is being written to the tape  400 . 
     The tape  400  comprises one or more embedded servo tracks  406  reserved for updated servo positioning information that is written to the tape  400  as data is being written to the data tracks  304  of the tape  400 . Since the one or more embedded servo tracks  406  are written into a data track  304 , the plurality of data tracks  304  and the one or more embedded servo tracks  406  have a same length on the tape  400 . The embedded servo tracks  406  may be written into one or more of the data channels or tracks  304  simultaneously as user data is being written to the data tracks  304 . The embedded servo tracks  406  may be erased and re-written as user data is erased and re-written from the tape  400 . Each subsequent re-write of the embedded servo track  406  will comprise updated TDS information or TDS effects on the tape  400 , allowing for the updated TDS information to be compared to the dedicated servo tracks  302 . A controller of a tape head (not shown) may receive and analyze the positioning information read from the embedded servo tracks  406 . 
     The positioning information stored in the embedded servo track  406  may include information of one or more parameters: servo busts, servo phase locked loop (PLL), environmental measurements, workload or wear counters, tape tension, friction, and tilt angle, among others. The positioning information and various parameters written in the embedded servo track  406  may be used to accurately append data to the data tracks  304 . 
     Similarly, the tape  450  is similar to the tape  350  of  FIGS.  3 B- 3 E ; however the tape  450  comprises an updated servo track  402  rather than the embedded servo fields  306 . In some embodiments, the tape  450  may also comprise the one or more embedded servo fields  306  of  FIGS.  3 B- 3 E  in addition to the updated servo track  402 . The updated servo track  402  comprises servo positioning information written into one or more of the dedicated servo tracks  302  of the tape  450  when user data is being written to the tape  450 . As such, at least one or more dedicated servo tracks  302  may be reconfigured into the updated servo track  402 , which is then re-written one or more times to include updated servo positioning information and parameters. The updated servo track  402  may be written into one or more of the dedicated servo tracks  302  simultaneously as user data is being written to the data tracks  304 . The updated servo track  402  may be erased and re-written as user data is erased and re-written from the tape  400 . A controller of a tape head (not shown) may receive and analyze the positioning information read from the updated servo track  402 . 
     The positioning information stored in the updated servo track  402  may include information of one or more parameters: servo busts, servo phase locked loop (PLL), environmental measurements, workload or wear counters, tape tension, friction, and tilt angle, among others. The positioning information and various parameters written in the updated servo track  402  may be used to accurately append data to the data tracks  304 . 
     By writing embedded servo information to a tape while writing user data to the tape, the tape head assembly can be controlled and positioned accurately, and new data can be appended accurately to the tape as well. The embedded servo information can be compared to dedicated servo tracks written to the tape at a factory level in order to determine whether the tape has changed or been deformed in any way and where data is actually located on a tape. Furthermore, various parameters and conditions of the tape can be easily determined by reading the embedded servo information, allowing for any corrections or tilting of the tape head assembly to be made dynamically as needed. 
     In one embodiment, a tape head assembly comprises one or more servo heads configured to read servo data from one or more dedicated servo tracks of a tape, a plurality of write heads configured to: write user data to a plurality of data tracks of the tape and write one or more embedded servo fields into one or more data fields of the plurality of data tracks of the tape, the one or more embedded servo fields comprising servo positioning information, and a plurality of read heads configured to read the user data and the embedded servo fields from the tape. 
     The positioning information stored in the one or more embedded servo fields comprises one or more parameters selected from the group consisting of: servo busts, environmental measurements, workload or wear counters, a tension of the tape, friction, and a tilt angle of the tape head. The one or more embedded servo fields are inserted periodically along a length of the tape. The one or more embedded servo fields have a consistent distribution along a length of the tape. The one or more embedded servo fields have an asymmetric distribution along a length of the tape. The plurality of read heads are configured to read the one or more embedded servo fields from the tape when appending data to the tape. The plurality of write heads are configured to write the one or more embedded servo fields simultaneously when writing user data to the tape. The one or more embedded servo fields are erasable and re-writeable. A tape drive comprises the tape head assembly and a controller configured to independently control each of the one or more servo heads, the plurality of write heads, and the plurality of read heads. 
     In another embodiment, a tape head assembly comprises one or more servo heads configured to read servo data from one or more dedicated servo tracks of a tape, a plurality of write heads configured to: write user data to a plurality of data tracks of the tape and write one or more embedded servo tracks into one or more data tracks of the tape, the one or more embedded servo tracks comprising servo positioning information, wherein the plurality of data tracks and the one or more embedded servo tracks have a same length, and wherein the one or more embedded servo fields are erasable and re-writeable, and a plurality of read heads configured to read the user data and the embedded servo fields from the tape. 
     The servo positioning information is used to determine a condition of the tape. Based on a condition of the tape, the servo positioning information is used to determine a tilt angle for the tape head assembly when reading the user data or appending new data to the tape. The plurality of write heads are configured to write the one or more embedded servo tracks when writing user data to the tape. The one or more embedded servo tracks can be re-written. A tape drive comprises the tape head assembly and a controller configured to independently control each of the one or more servo heads, the plurality of write heads, and the plurality of read heads. 
     In yet another embodiment, a tape drive comprises a tape head assembly comprising: one or more servo heads configured to read servo data from one or more dedicated servo tracks of a tape, a plurality of write heads configured to: write user data to a plurality of data tracks of the tape and write embedded servo positioning information into one or more data fields of the plurality of data tracks of the tape, and a plurality of read heads configured to read the user data and the embedded servo positioning information from the tape. The tape drive further comprises a controller coupled to the tape head assembly, the controller configured to: dynamically tilt the tape head assembly based on the read embedded servo positioning information, and determine where to append new data to the plurality of data tracks based on the read embedded servo positioning information. 
     The embedded servo positioning information is used to determine whether the tape has been expanded or compressed. The embedded servo positioning information comprises one or more parameters selected from the group consisting of: servo busts, environmental measurements, workload or wear counters, a tension of the tape, friction, and a tilt angle of the tape head. The embedded servo positioning information is written over a dedicated servo track of the tape when writing user data to the tape. The embedded servo positioning information is written to one or more data fields of one or more data tracks of the tape when writing user data to the tape. The embedded servo positioning information is compared to the dedicated servo tracks when dynamically tilting the tape head assembly and when determining where to append the new data. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.