Patent Document

CLAIM TO PRIORITY 
   This application claims priority to copending United Kingdom utility application entitled, “Method and Apparatus for Recording Data onto a Recording Medium Including Warning of the Approach to an End of Medium Position,” having serial number GB 0409643.4, filed Apr. 30, 2004, which is entirely incorporated herein by reference. 
   TECHNICAL  
   The present disclosure relates to a method and apparatus for recording a sequence of data onto a recording medium having a recording capacity up to an end of medium position, and more specifically to providing a warning of the approach to the end of medium position. 
   BACKGROUND 
   In order to store digital electronic data, it is known to use magnetic tape data storage cartridges which are inserted into a tape drive unit having magnetic recording and reproducing heads. Typically such magnetic storage devices are used for recording back-up data generated by a host computer programmed to control the data recording process. 
   In recording a sequence of data sets onto a magnetic data recording medium such as the tape in a tape cartridge, it is conventional to provide the host computer with an early warning of the end of the recording medium (EWEOM). The position of the EWEOM has to be chosen judiciously so as to avoid writing data beyond the capacity provided by the recording medium and yet avoid unnecessarily limiting the capacity of the recording medium to record data. 
   Some data processing operations require that the data to be recorded is copied from one recording medium onto another recording medium. Such operations may, for example, be required to make an archive record or to provide a back up of data to be used at a plurality of different sites. A problem arises in the case of magnetic storage tapes because the data storage capacity of a tape may vary due to a number of factors, including the magnetic recording quality of the tape, and of the drive and a combination of the two. The nominal capacity of two tapes may be the same but they may actually vary in capacity by up to 5 to 10%. 
   This means that the ability to perform a tape to tape copying operation may be compromised if the source tape from which the data is to be copied is filled up to or close to its capacity. This is because the destination tape onto which the data is to be recorded may not have a capacity sufficient to receive all the data. 
   A prior solution to this problem has been to make the position at which the EWEOM is given to the host further removed from the real end of medium position on the tape. This only helps if the host performing the tape to tape copying operation continues recording on the target tape after the EWEOM has been reported to the host. This solution runs the risk that the real end of medium position will be encountered and at this point the copy operation will have failed. 
   Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies. 
   SUMMARY 
   According to the present disclosure, there is now provided various embodiments of systems and methods of recording data in a sequence of data sets onto a data recording medium having a recording capacity up to an end of medium position. Briefly described, one embodiment of a method includes the following steps: deriving a logical count of the amount of data recorded on the recording medium, and comparing the logical count to a reference value to generate a warning of an approach to the end of medium position. 
   Embodiments of the present disclosure also provide systems for recording data in a sequence of data sets onto a data recording medium having a recording capacity up to an end of medium position. One embodiment of such a system includes an apparatus having counting logic to derive a logical count of the amount of data recorded on the recording medium, and comparing means to compare the logical count to a reference value so as to generate a warning of an approach to the end of medium position. 
   Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present disclosure will now be described, by way of example only, with reference to the accompanying drawings in which; 
       FIG. 1  is a block diagram of the hardware components and interconnections of a data storage system according to the present disclosure, 
       FIGS. 2 and 3  show a tape cartridge included in the system of  FIG. 1 , 
       FIG. 4  is a block diagram of transponders and memory included in the data storage apparatus of  FIG. 1 , 
       FIGS. 5 ,  6 ,  7  and  8  are diagrams of data recording on a tape included in the tape cartridge of  FIGS. 2 and 3 , and 
       FIG. 9  is a flow diagram illustrating steps in a method embodying the present disclosure. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , there is shown a data storage apparatus incorporating a tape drive  10  and a controller  12  coupled to at least one hierarchically superior host  11 . The controller  12  is connected to the host  11  by an interface  13 . The tape drive  14  includes a drive engine  15  and a drive mechanism  16  that receives a tape cartridge  17  that has a cartridge memory  18 . A controlling software application on the host  11  acts through the controller  12  to control the tape drive  14  to read data from and write data to the tape storage cartridge  15 . 
   The host system  11  has at least one central processing unit (CPU) and a memory to store the controlling software application. The interface  13  connecting the host system  11  to the data storage apparatus  10  is, in some embodiments, a Small Computer Systems Interface (SCSI) or a USB (Universal Serial Bus). The method of communication over either of these standard busses is known to those skilled in the art. 
   The drive mechanism  16  includes electrical and mechanical components that receive, position, and access tape cartridges. The drive mechanism has components to lock a tape cartridge in place, an ejection motor, and read/write heads. The drive engine  15  is a data processor that is programmed to supervise the operation of the drive mechanism  16  and to manage the flow of data to be recorded in or read from a tape cartridge  17  received in the drive  14 . A register  42  in the drive tape drive  14  holds an EWEOM reference value that represents a reference logical position along the tape at which an EWEOM is to be sent to the host  11  as will be described below. 
     FIGS. 2 and 3 , show a general view of the cartridge  17  including a structural casing  19  within which are located the cartridge memory  18  and a magnetically recordable tape. The cartridge is an implementation of Linear Tape Open (LTO) technology. The tape is supported on a rotatable tape reel or spool and has a leader by means of which the tape drive  14  can uncoil and withdraw the tape from the cartridge reel or spool for data reading or recording. 
   Referring to  FIG. 4 , the cartridge memory  18  includes a transponder  21  and a memory area  18   a  that has the capability of non-volatile storage and is, in some embodiments, an EEPROM (electronically erasable programmable read only device). The transponder  21  consists of a transmitter  22 , a receiver  23 , an aerial  24  and a processor  25 . The cartridge memory  18  co-operates with a transmitter/receiver module  26  incorporated into the tape drive  14 . The module  26  includes a serial interface  27  to the tape drive, a processor  28 , a transmitter  29 , a receiver  30  and an aerial  31 . The transponder  21  incorporated into the cartridge  17  is inductively powered by the transmitter/receiver module  26  and data is exchanged between the transmitter/receiver  22 ,  23  of the transponder  21  and the transmitter/receiver  29 ,  30  of the module  26  by way of the inductively coupled aerials  24  and  31 . The aerials  24  and  31  thus provide a contactless coupling of the cartridge memory  18  to the tape drive  14  for data transfer between the cartridge memory and the tape drive when the tape cartridge  17  has been received by the tape drive. 
   The cartridge memory area  18   a  stores information including usage information, cartridge manufacturer information, and cartridge memory manufacturer information. The cartridge manufacturer information includes the cartridge type, a serial number of the cartridge, and an identification of the manufacturer. The cartridge memory manufacturer information includes the serial number of the transponder, the type of transponder, and the serial number of the cartridge memory. 
     FIGS. 5 and 6  are diagrammatic representations of the manner in which data is recorded on the tape. Each of  FIGS. 5 and 6  show a short portion only of the tape. There are five servo bands  32  pre-recorded on the tape that are used for track following while the cartridge is being operated in the cartridge drive  14 . The servo bands are written before the cartridge is usable for data storage and are located at predefined specific distances from one edge of the tape that is referred to as the tape reference edge. Each servo band contains servo frames encoded as longitudinal position words to provide an indication of the position down the length of the tape. In an exemplary embodiment, the longitudinal position words each comprise 36 servo frames which increment in value as the tape is removed from the cartridge in the forward direction within a range from 0 to 7,529,535. 
   Each of the four areas between adjacent pairs of servo bands is a data band  33 —the bands being numbered  2 ,  0 ,  1  and  3  respectively with data band  2  being nearest to the tape reference edge and data band  3  being furthest from the tape reference edge. The four data bands each have 128 data tracks arranged in eight data sub-band s as shown in  FIG. 6 . The 16 data tracks in a sub-band are accessed in a spiral manner in forward and reverse wraps. Forward wraps are recorded while the tape is moving from the beginning of the tape to the end of the tape and reverse wraps are recorded while the tape is moving from the end of the tape to the beginning of the tape. The end of medium position of the tape is the end of the last data sub-band  7  of the data band  3 . An early warning of end of media (EWEOM) is provided to the host  11  on the approach to the end of medium position of the tape in the tape cartridge  17  as will be described below. 
     FIG. 7  shows the way in which data is transformed as it flows from the host  11  to the recorded tape. The data conforms to a data format in which data is logically divided into records  34  and file marks. Each record  34  is processed by the host to compute a cyclic redundancy check (CRC) character  35  that is added to the record to form a protected record  36 . The CRC character is useful in the detection of errors. A data compression algorithm processes the protected records  36  and file marks to produce a stream of symbols  37  broken into sets of host data  38  to which a data set information table (DSIT)  39  is added. The host data and data set information table (DSIT)  39  together constitute a data set  40 . 
     FIG. 8  shows the tape laid out in diagrammatic form from the beginning of the tape labelled BOT to the end of the tape labelled EOT. Data sets are recorded along the tape beginning with a format identification data set FID, followed by user data sets, and ending with an end of data set labelled EOD. A blank unrecorded portion  41  of the tape extends from the end of data set EOD to the end of the tape EOT. As will be appreciated, the end of tape EOT shown in  FIG. 8  is reached at the end of the last data sub-band. An early warning of end of media (EWEOM) is provided to the host  11  if the length of the blank portion  41  of tape left between the end of data EOD and the end of tape EOT is reduced to a predetermined physical lower limit. At this point, the host  11  will terminate the recording operation. This position-based EWEOM is generated by means that sense the diameter of the tape in the cartridge  17  and, hence, how far the tape has advanced in the cartridge  17  during recording the last data sub-band. An alternative way of generating a position-based EWEOM is to detect pre-recorded data signifying the end of media at a prescribed position along the tape. 
   A recording session that depends solely on a position-based EWEOM suffers from the disadvantage that the provision of the EWEOM is at a fixed position relative to the end of the record. The position-based EWEOM thus provides no flexibility over the position along the tape at which the EWEOM is provided to the host. Data can be recorded on the tape in the tape cartridge  17  until the EWEOM is provided to the host  11 . 
   The host  11  is able to control more than one tape drive so as to manage the flow of data to be copied from a source tape in one tape cartridge onto a destination tape in another tape cartridge. If the source tape is filled with data, then it is possible that the destination tape may not be able to accommodate all the data from the source tape. This is because the data storage capacity of the destination tape may be less than that of the source tape, even though the two tapes may have the same nominal capacity. The discrepancy results from the variable magnetic recording quality of the tape, and of the drive, and a combination of the two. The variation in capacity of a tape may be up to 5 to 10%. 
   To overcome these difficulties, an additional EWEOM is generated that is based on the amount of data that is recorded on the destination tape. A logical count of the amount of data is calculated in the tape drive  14  as the sum of records received from the host  11  from the start of the tape up to the current position. When each data set is filled, the drive puts the current count of records and file marks into the DSIT for the data set so that it is possible to identify a specific logical position from the DSIT. The logical count is registered in the cartridge memory  18  to indicate the logical position of the recording along the tape. When appending further data to the tape, the tape drive resumes the count from the logical position of the append point. 
   A register  42  in the drive tape drive  14  holds an EWEOM reference value that represents a reference logical position along the tape at which an EWEOM is to be sent to the host  11 . The drive  14  is programmed to continuously compare the logical count representing the logical position from the start of the tape with the EWEOM reference value in the register  42 . If the logical count reaches the same value as the EWEOM reference value, the drive  14  generates an EWEOM signal that is sent to the host  11 . At that point the host  11  will terminate the recording operation. 
   The EWEOM reference value represents the amount of data that can be recorded on the destination tape before an EWEOM is generated. The tape drive is programmed to enter that value as a preliminary to the recording operation. The reference value, and therefore the amount of data that it represents, can be varied by program control according to the amount of data on the source tape and the expected capacity of the destination tape. As already explained, the capacity of the destination tape can vary depending on factors such as the recording quality of the destination tape. A degree of flexibility is thereby provided over when an EWEOM is generated to take account of the amount of data stored on the source tape and the capacity of the destination tape. 
     FIG. 9  illustrates the program routine for writing data to the tape. In a first step  43 , the EWEOM reference value is entered into the register  42 . In step  44 , the count representing the current logical position is extracted from the cartridge memory  18  and compared in step  45  to check if the count is less than the reference value. If the result of the comparison is positive, the process continues to step  46 . In the step  46 , the length of blank tape is compared to the lower limit and if the comparison is positive, the process returns to step  44 . If the result of the comparison is negative in step  45  or step  46 , an EWEOM is returned to the host  11  and recording is terminated. 
   What has been described are systems and methods to record data keeping account, as the data is recorded, of the amount of data that has been recorded on the data recording medium, and providing a warning of the approach to the end of medium position when the amount of data that has been recorded reaches a predetermined amount. The determination of the amount of data is intended to provide an indication of the logical position along the tape up to which the recording has progressed. This determination may be made by reference to a count of the records that have been recorded. Alternatively, the determination may be made from the number of frames within the recording or by monitoring the amount of data that has been processed by the tape drive either before or after data compression. 
   It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the present disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the present disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

Technology Category: 3