Patent Publication Number: US-2011051277-A1

Title: Method for erasing magnetic tapes

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/237,351, entitled “Method for Erasing Magnetic Tapes”, filed Aug. 27, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method for erasing magnetic tapes. 
     2. Description of the Related Art 
     Current secure erasure of data on magnetic media requires demagnetization, degaussing or overwriting of the written information on a tape. All methods and operations that do not use a data write/read capable tape transport destroy the ability to reuse the media as the factory written format is lost in these operations. The currently available methods for data erasure, while capable of rendering the tapes re-useable without readily detecting residual data, do not remove enough of the residual data on the tapes to make the tapes “secure” from the perspective of many of the legal requirements currently attempting to control the escape of private information. 
     The attributes of the tape technology of interest to the application of this method are described in a number of publications. Concise reviews of state of the art technology for tape formats and recording heads are described in G. A. Jaquette, “LTO: A Better Format for Mid-Range Tape”,  IBM Journal of Research &amp; Development , Vol. 47, No. 4, pp. 429-444, 2003; E. R. Childers, et al., “Six Order of Magnitude in Linear Tape Technology: The One-Terabyte Project”,  IBM Journal of Research &amp; Development , Vol. 47, No. 4, pp. 471-482, 2003; and R. G. Biskeborn and J. H. Eaton, “Hard Disk Drive Technology Flat Heads for Linear Tape Recording”,  IBM Journal of Research &amp; Development , Vol. 47, No. 4, pp. 385-400, 2003, all of which are incorporated herein by reference. 
     With the current deficiencies in the technology relating to the erasure of tapes, a need exists for a method and system which can securely overwrite the residual data on a tape to a precision currently not practiced on operational tape transports. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a method for securely erasing residual data on a magnetic tape formatted with a plurality of servo patterns providing boundaries between a plurality of data bands containing data that is recorded thereon during normal write operations, the data being written on many adjacent data tracks that run parallel to an edge of the magnetic tape. The method includes identifying a first edge of each of the plurality of servo patterns and erasing a portion of each of the plurality of data bands during a first pass of a tape head as it moves in a first direction. The method further includes the step of indexing the tape head to identify an opposite second edge of each of the plurality of servo patterns and erasing a different portion of each of the plurality of data bands during a second pass of the tape head as the tape head moves in a second direction opposite the first direction. 
     It is another object of the present invention to provide a method wherein the tape head includes a servo read element capable of following the servo patterns. 
     It is a further object of the present invention to provide a method wherein the plurality of servo patterns are servo bands. 
     It also an object of the present invention to provide a method wherein the plurality of data bands includes four data bands that are simultaneously erased by the tape head. 
     It is another object of the present invention to provide a method wherein the tape head includes a plurality of erase elements spread along a length of the tape head. 
     It is a further object of the present invention to provide a method wherein each of the erase elements is shaped and dimensioned to at least overwrite half of a data band. 
     It is also an object of the present invention to provide a method wherein the tape head includes a plurality of servo read elements, and the method includes the step of monitor tape erasure as the tape is being erased. 
     It is another object of the present invention to provide a method wherein the step of identifying the first edge of each of the plurality of servo patterns and erasing a portion of each of the plurality of data bands during a first pass of the tape head as it moves in the first direction includes erasing a first half of each of the plurality of data bands. 
     It is a further object of the present invention to provide a method wherein identifying the opposite second edge of each of the plurality of servo patterns and erasing a different portion of each of the plurality of data bands during the second pass of a tape head as the tape head moves in a second direction opposite the first direction includes erasing an opposite second half of each of the plurality of data bands. 
     Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which taken in conjunction with the annexed drawings, discloses a preferred, but non-limiting, embodiment of the subject invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 ,  2  and  3  are schematics showing LTO format on a magnetic tape. 
         FIG. 4  is a schematic showing erasure of a magnetic tape in accordance with the present invention. 
         FIGS. 5 ,  6 A and  6 B are schematics showing a tape head and operation thereof in accordance with the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The detailed embodiment of the present invention is disclosed herein. It should be understood, however, that the disclosed embodiment is merely exemplary of the invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as a basis for teaching one skilled in the art how to make and/or use the invention. 
     In accordance with the present invention, and with reference to  FIGS. 1 ,  2 ,  3 ,  4 ,  5 ,  6 A and  6 B, a method for securely erasing (or overwriting) residual data on a magnetic tape  10  to a precision currently not practiced on operational tape transports is provided. In general, the present invention provides a mechanism by which the factory written servo format is followed as the magnetic tape is spooled out of a cartridge. A broad width erase head is run down the magnetic tape holding the erase element of the tape head within 1-2 microns of the edge of the formatted servo band. Upon reaching the end of the magnetic tape, the tape head is either moved down to follow the next servo band or a separate set of erase elements in the fixed structure of the tape head (two potential ways to do this) are turned on so as to overlap the previously overwritten band of data tracks and complete erasure of data tracks within 1-2 microns of the upper edge of the servo format band. 
     Briefly, the present invention provides a method for securely erasing residual data on a magnetic tape  10  formatted with a plurality of servo patterns  18  providing boundaries between a plurality of data bands  28   a - d  containing data that is recorded thereon during normal write operations, the data being written on many adjacent data tracks  20  that run parallel to an edge  10   a,    10   b  of the magnetic tape  10 . The method includes identifying a first edge  24   a  of each of the plurality of servo patterns  18  and erasing a portion (for example, a first half) of each of the plurality of data bands  28   a - d  during a first pass of a tape head  12  as it moves in a first direction. The method further includes the step of indexing the tape head  12  to identify an opposite second edge  24   b  of each of the plurality of servo patterns  18  and erasing a different portion (for example, an opposite second half) of each of the plurality of data bands  28   a - d  during a second pass of the tape head  12  as the tape head  12  moves in a second direction opposite the first direction. 
     In accordance with the present invention, currently available commercial tape drives are modified for the purpose of data eradication, not data reading or interchange. Custom built magnetic tape heads  12  are used to precisely track the existing servo format on the magnetic tape  10 , but rather than contain complex data write/read elements, the magnetic tape heads  12  employed in accordance with the present invention contain multiple wide erase elements  14  capable of creating a higher AC erase field than typical data erasure heads used in the normal operational data processing heads in the drives. 
     Since closely packed erase elements are not required for the broad area overwrite employed in accordance with the present invention, as compared to applications requiring writing discrete narrow tracks in close proximity during data writing, more turns can be used in the electromagnet of the tape head used in accordance with the present invention. The greater the number of turns on the coil of the erase element, the higher the magnetic field. In addition, since rapid creation of reversed magnetic fields (ones and zeros) in data writing is not needed for implementation of the present invention, the magnetic field created by the erase element can be sustained at peak levels during erasure. This is well known to those skilled in the art for dedicated “erase” heads and is covered in several patents on erase head design, such as, U.S. Pat. No. 6,894,869, to Dugas, Advanced Research Corporation, May 17, 2005, entitled “Low inductance, ferrite sub-gap substrate structure for surface film magnetic recording heads”, U.S. Pat. No. 7,009,810, to Dugas, Mar. 7, 2006, entitled “Thin-film magnetic recording head having a timing-based gap pattern for writing a servo track on magnetic media”, U.S. Pat. No. 7,256,962, to Tateishi, Aug. 14, 2007, “Magnetic tape drive with AC erase element upstream from plural head elements”, U.S. Pat. No. 7,492,550, to Samofalov et al., Feb. 17, 2009, entitled “Magnetic recording head and method for high coercivity media, employing concentrated stray magnetic fields”, all of which are incorporated herein by reference. 
     Servo read elements  32   a,    32   b  are only provided on the leading and trailing edges of the wide erase structures, that is, the erase elements  14 , so as to verify the overwrite and track position relative to the servo position error signal. The existing servo detection capabilities of the tape drives and embedded, standard operational protocols are used to exercise the magnetic tape and perform the track following operation. It should be appreciated that since no data is written or read in accordance with the present invention, none of the proprietary embedded functions of the tape drives would be used and implementation of the present invention should not violate the intellectual property rights of others. 
     In accordance with a preferred implementation of the present invention, a blank commercial magnetic tape  10  is factory formatted with servo patterns  18  on the tape which provide boundaries between which data that is recorded thereon during normal write operations. For the purposes of explaining the present invention, the Ultrium™ LTO format is used as a representative example in  FIG. 1 . However, and as those skilled in the art will certainly appreciate, other formatting protocols may be employed without departing from the spirit of the present invention. 
     Published standards describe the servo formats and interchange attributes for the various tapes of interest as subjects for the application of the present method for data erasure and tape reuse. For example, the servo formats and interchange attributes described in the following publications could be employed in the implementation of the present invention: ECMA Standard 196, “Data Interchange on 12.7 mm 36-Track Magnetic Tape Cartridges”, December 1993; ECMA Standard 278, “Data Interchange on  12 . 7  mm  128 -Track Magnetic Tape Cartridge—Parallel Serpentine Format”, 2 nd  Edition, June 2000; and ECMA Standard 319, “12.7 mm 383-Track Magnetic Tape Cartridges—Ultrium-1 Format”, June 2001, all of which are incorporated by reference. 
     As those skilled in the art will certainly appreciate, when data is written to magnetic tape  10  using linear tape recording, the data is written on many adjacent data tracks  20  that run parallel to the edge of the magnetic tape  10 . In fact, using digital tape technology it is possible to write many data tracks  20  across a single magnetic tape  10 . This allows users to store large amounts of data along a limited quantity of magnetic tape  10 . Since many data tracks  20  are written across a single strand of the magnetic tape  10 , it is necessary to provide a track-following servo, that is, a mechanism that allows a tape head  12  to dynamically follow a tape data track  20 . A tape drive  22  using a track-following servo will constantly move the tape head  12 , the component that actually performs the read, write and erase functions, and align it to the desired data track  20 . 
     When implementing the LTO format in magnetic tape, electronic signals are generated through the real-time reading of servo data bands (or servo tracks)  24  that are prerecorded on the LTO tape. Servo tracks  24  enable accurate positioning of the tape heads  12  of the tape drive  22  over the data track  20 , ensuring that the tape head  12  does not stray onto an adjacent data track  20 . They are necessary to support high-data densities on the magnetic tape  10  where the data tracks  20  are extremely close together. The servo bands  24  are written when the cartridge in which the magnetic tape  10  is mounted is manufactured, before the cartridge is usable for data storage and retrieval. If the servo bands  24  are erased, the magnetic tape  10  becomes unusable. 
     With reference to the example of an LTO formatted magnetic tape  10 , as shown in  FIG. 2 , five servo bands  24 , numbered  0  through  4 , make up the servo tracking mechanism on the LTO Ultrium magnetic tape  10 . They are each located at specific distances from the tape references edge  26 . 
     Referring to  FIG. 3 , the area between adjacent servo bands  24  is a data band  28   a - d . There are four data bands  28   a,    28   b,    28   c,    28   d,  where data band  28   a  is nearest to the tape references edge  26  of the magnetic tape  10  and data band  28   d  is farthest away. Each data band  28   a - d  includes a number of data tracks  20  that are simultaneously recorded from one end of the magnetic tape  10  to the other end in a manner well known to those skilled in the art. 
     The recording format employed in conjunction with Ultrium LTO format has a serpentine characteristic. The mechanism employed in the tape drive  22  allows the tape head  12  to make multiple passes from the beginning of the magnetic tape  10  to the end of the magnetic tape  10  and back to read, write or erase the full capacity of the magnetic tape  10  maintained within the data cartridge. For example, different levels of data density are possible when employing the Ultrium LTO format; the Ultrium 1 format allows for 384 data tracks to be split into four data bands of 96 data tracks each, the Ultrium 2 format allows for 512 data tracks to be split into four data bands of 128 data tracks each, the Ultrium 3 format allows 896 data tracks to be split into four data bands of 224 data tracks each. 
     When implementing the present method, all four data bands  28   a - d  are simultaneously erased by tape head  12  constructed in accordance with the present invention and shown below with reference to  FIG. 4 . More particularly, and in accordance with a preferred embodiment of the present invention, the tape drive  22  includes a tape head  12  having four erase elements  14  spread along the length of the tape head  12 . The erase elements  14  are shaped and dimensioned on the tape head  12  to overwrite at least half of the data band  28   a - d  region of the tape format that exists between each servo band  24 . It should be appreciated the erase elements are sized to create a slight erasure overlap as the erase elements  14  erase the data bands  28   a - d  during the inbound pass and outbound pass as discussed herein so that the erasure of each data band  28   a - d  is complete. However, it should be understood the erase element  14  may not overlap the servo band  24  so as to protect the servo band  24  from inadvertent erasure. 
     In the implementation of the present invention in the LTO example discussed above, four erase elements  14  are built into the tape head  12  to simultaneously erase or overwrite one half of each of the four data bands  28   a - d  (for example, 48 data tracks on each data band of an Ultrium 1 format magnetic tape, 64 data tracks of each data band of an Ultrium 2 format magnetic tape, and 112 data tracks of each data band of an Ultrium 3 format magnetic tape). As a result, one half of all four data bands  28   a - d  are erased on each pass of the tape head  12  as depicted in the diagram in  FIG. 4 . 
     As such, and in accordance with a preferred embodiment of the present invention, when the cartridge in which the magnetic tape is supported is inserted into the drive mechanism  22 , a threading mechanism of the drive mechanism  22  pulls the leader pin and attached tape out of the cartridge, across the tape head, and onto a non-removable take-up (machine) reel. The tape head  12  can then erase data from or to the magnetic tape  10 . The present invention is directed to the erasure of standard magnetic tapes, and consequently the basic structure of the drive mechanism and the cartridge will be the same as currently employed and well known to those skilled in the art. For example, such structures are disclosed in U.S. Pat. Nos. 7,453,361, to Findlay, Nov. 18, 2008, entitled “Refurbishing and resale techniques for data storage tape”, 7,304,576, to Findlay, Dec. 4, 2007, entitled “Refurbishing and resale techniques for data storage tape”, 7,256,962, to Tateishi, Aug. 14, 2007, entitled “Magnetic tape drive with AC erase element upstream from plural head elements”, 6,707,630, to Doi et al., Mar. 16, 2004, entitled “Method for managing life of a storage medium, storage device, storage system, and storage medium”, 6,385,557, to Mundo, May 7, 2002, entitled “Tracking the remaining useful like of a magnetic data storage tape”, 5,426,543, to Dy et al., Jun. 20, 1995, entitled “Servo positioning system for magnetic recording media”, 5,229,895, to Schwarz et al., Jul. 20, 1993, entitled “Multi-track servo recording head assembly”, and 4,631,479, to Haga, Dec. 23, 1986, entitled “Error locator for high-speed inspection of magnetic tape”, the relevant disclosures of which are incorporated herein by reference. 
     At this point the magnetic tape  10  is moved in a first, or forward, direction relative to the tape head  12  and the respective four erase elements  14  of the tape head  12  erase (or overwrite) half the data tracks  20  (that is one half of the data band  28   a - d ) between the servo bands  24  on one edge of all the servo bands  24  on the outbound pass. Upon reaching the logical end of the magnetic tape  10  (which is encoded into the operational software using format length statements already written on the magnetic tapes  10  by the tape producer and stated in standards for these formats and as such are in the public domain) the tape head  12  is indexed so as to position the respective four erase elements  14  over the remaining data tracks  20  (that is, the other half) adjacent the opposite servo band  24 , that is, the opposite side of the data band  28   a - d . As a result, the entire magnetic tape  10  is erased or overwritten in one full file pass of the magnetic tape  10 . This allows an acceptable time (less than 5-6 minutes) to perform the entire data erasure operation. 
     Since data is not read or written in the operation of the tape drive  22  employed in accordance with the present invention, but the data bands  28   a - d  are only monitored to confirm no residual patterns of the original data, the magnetic tape  10  would run at the maximum speed at which the drive  22  can reliably run while following the servo format which is typically significantly faster than normal drive operation during data write or read operations. 
     As is well known to those skilled in the art, track following servo readers  30  would be placed in the tape head  12  to achieve optimum position error detection and response to the head actuator to maintain optimum on track guiding during the operation at the highest possible tape speed. 
     The present invention provides for the enablement of one device to process multiple tape formats. In particular, since the application of the present invention is for generic tape processing, the restrictions imposed by various restrictive tape formats for write compliance are not applicable and the devices used for this process do not need to recognize these restrictions. As a result, one format overwrite processing capable device can erase data on all formats with a compatible servo pattern. 
     The erasure of the data is also verified as the tape head  12  is moved across the magnetic tape  10 . In particular, the tape head  12  is provided with servo read elements  32   a,    32   b  for monitoring the magnetic tape  10  to ensure that all data is erased in accordance with the present invention. More particularly, and as briefly discussed above, servo read elements  32   a,    32   b  are built into the tape head  12  so that they may monitor the erasure magnetic tape  10  as the magnetic tape  10  is moved across the tape head  12  in accordance with the present invention. Referring to  FIG. 5 , the positioning of the servo read elements  32   a,    32   b  and erase elements  14  is repeated across the span of the tape head  12  as needed to follow the top and bottom edges  24   a ,  24   b  of the servo band  18  during the outbound motion of the magnetic tape  10 . In accordance with a preferred embodiment, a pair of servo read elements  32   a,    32   b  is located adjacent a top side  14   a  of each erase element  14  with the respective servo read elements  32   a,    32   b  located on the left side  14   b  and right side  14   c  of the erase element  14  and a pair of servo read elements  32   a,    32   b  is located adjacent a bottom side  14   d  of each erase element  14  with the respective servo read elements  32   a,    32   b  located on the left side  14   b  and right side  14   c  of the erase element  14 . It should be appreciated the terms left, right, top and bottom are relative terms dependent upon the perspective from which one views the various elements and this description is provided with reference to  FIG. 5 . Ultimately, the erase element  14  is “sandwiched” between the servo read elements  32   a,    32   b  so the same tape head  12  can be used for both erasure and verification as discussed below in greater detail. On the return motion of the magnetic tape  10  back into the cartridge, a duplicate pair of servo read elements  32   a ,  32   b  not active during the outbound motion is electrically switched so as to perform the same operation in the reverse direction. 
     In particular, and with reference to  FIGS. 6A and 6B , servo read elements  32   a  (trailing) monitor the erasure quality and servo read elements  32   b  (leading) actively follow either the top or bottom edge  24   a,    24   b  of the servo band  24  when the tape moves in the first direction shown in  FIG. 6A  and servo read elements  32   b  (trailing) monitor the erasure quality and servo read elements  32   a  (leading) actively follow the top or bottom edge  24   a,    24   b  of the servo band  24  when the tape moves in the opposite second direction shown in  FIG. 6B . As shown in accordance with a preferred embodiment as shown with reference to  FIG. 4 , the read elements  32   a,    32   b  positioned adjacent the top of the erase elements  14  follow the bottom edges  24   b  of the servo bands  24  on the outbound pass (with the read element  32   a  trailing and read element  32   b  leading) and the read elements  32   a,    32   b  positioned adjacent the bottom of the erase elements  14  follow the top edges  24   a  of the servo bands  24  on the outbound pass (with the read element  32   b  trailing and read element  32   a  leading) after the tape head  12  has been indexed. 
     It should be appreciated the ability of the trailing read element  32   a,    32   b  to read, and thereby monitor, the data tracks for monitoring erasure quality after erasure while the erase is going on is important to provide concurrent verification of erasure. 
     As those skilled in the art will certainly appreciate, the drive mechanism employed in accordance with the present invention may be constructed in a variety of manners depending upon the specific requirements (for example, depending upon performance and specification requirements, such as, the desired erasure rate or quality design points) of different manufacturers without departing from the spirit of the present invention. 
     While the preferred embodiments have been shown and described, it will be understood that there is no intent to limit the invention by such disclosure, but rather, is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention.