Abstract:
Separations between the end of one data file and the beginning of the next data file are recognized, without utilizing an entire data storage block by means of a controlling program for a peripheral recording device monitoring the control information headers of helically stored data on a recording tape. When files are stored on the recording tape, the controlling program increments an increase of a file section number by one and increments to zero a data block number at the beginning of a new data file. When the recording device is reading the recording tape and there is detected an incrementation of the file section number and a zero value for a data block number, a recognition is made that this data indicates the end of one data file and the beginning of another data file.

Description:
TECHNICAL FIELD 
     The present invention relates to the storage of blocks of data on a tape, and more specifically to a method of identifying separations between adjacent data files stored on a tape such as magnetic tape. 
     BACKGROUND OF THE INVENTION 
     Normally, when information data files are stored on tape such as a magnetic tape, individual files are separated by areas on the tape known as file marks. A file mark is a block of information on the tape containing predefined standards for identifying the file boundary but normally contains no information regarding the data files the mark is separating. Thus, the mark merely acts as an indicator of the ending of one data file and the beginning of another data file. 
     Information Data Files consist of a number of physical data blocks which are the minimum recordable entity. A data file may consist of one or more individual physical data blocks. A file mark separating two data files must be recorded over an entire physical data block since presently available recording devices are not capable of recording into a smaller entity. Therefore, where data files on a magnetic tape substantially consist of only one or two physical data blocks, each separated by a file mark, the area available on the tape for the storage of user data will be drastically reduced. 
     Thus, a need has arisen for a method to indicate the separations between adjacent data files without utilizing an entire block of data storage space. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the foregoing and other problems associated with the prior art by utilizing a transparent file mark with helically recorded data on a magnetic tape. The method utilizes the controlling software of the peripheral recording device to store data block and data file information within the control information header located in each helical track and in horizontal tracks located both above and below the helical tracks. 
     The control software of the peripheral recording device includes instructions to store two numbers in the control information header which together act as a file mark. These are the File Section Number (FSN) and the Data Block Number (DBN). When a new data file is started, the existing file section number is incremented by one and the existing data block number is set to zero. Later, when the peripheral recording device is actuated to read data from the tape instead of writing to the tape, the recording device interprets an incrementation of the FSN and the zeroing out of the DBN as an indication of a new file. Thus, the equivalent of a file mark is created without requiring an entire block of data space to be utilized as a file mark. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following detailed description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a diagram of the prior art method for volume formatting; 
     FIG. 2 is a diagram of the format of a system zone on a magnetic tape; 
     FIG. 3 is a diagram of the format of a partition on a magnetic tape; 
     FIG. 4 is a flow diagram of the process for formatting a partition that ,would be located across a system zone; 
     FIG. 5 is a flow diagram of the process to format the last partition at the end of a magnetic tape; 
     FIG. 6 is a flow diagram of the process to format a system zone which should extend beyond the end of the magnetic tape; 
     FIGS. 7A-7C illustrates the Pack, Waste and Stretch volume format options; 
     FIG. 8 illustrates the prior art use of file marks; 
     FIG. 9 is a schematic diagram of a magnetic tape with helically and longitudinally recorded information; and 
     FIG. 10 is an illustration of a magnetic tape utilizing transparent file marks. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to FIG. 1 wherein there is shown an illustration of the prior art formatting of the length of a magnetic tape for data storage. Under prior methods, a single system zone 2 is placed at the beginning of a magnetic tape 4. This zone contains the information necessary for system use during loading and threading operations. The system zone 2 is immediately followed by a single partition 6 starting at the beginning of media (BOM) and continuing until the end-of-media warning (EMW). The area for user data storage begins at the partition boundary 8. 
     In the present invention, at the beginning of the format procedure, the controlling software instructs a peripheral recording device to prompt a host computer system for the desired number of system zones and for the tape length interval between the system zones. System zones are fixed-length areas on tape, occurring at regular intervals, which are reserved for system use. The system zones are formatted onto the magnetic tape by the peripheral recording device as indicated by the responses of the host computer system. Once the plurality of system zones have been formatted onto the tape, system loading and threading operations may be carried out at any of the system zones. The peripheral recording device and the host computer system are conventional hardware and do not form a part of the present invention. 
     The format of a system zone is illustrated in FIG. 2. The system zone is comprised of two areas. The Load Operation Zone (LOZ) 3 is used during loading and unloading of the tape from a peripheral recording device. The Volume Format Information Zone (VFI) 5 is an area containing information on the data volume format. This information allows the peripheral recording device to locate any partition on the magnetic tape. All system zones contain substantially identical information. 
     At the same time the system zones are being formatted, the magnetic tape is also being formatted with a plurality of partitions. This process is initiated by a prompt from the controlling software of the peripheral recording device to the host computer system requesting the number of partitions and the length of partitions to be formatted onto the magnetic tape. The software also instructs the peripheral recording device to request the host computer system to choose a Pack, Waste, or Stretch format option. The software then formats partitions onto the tape in accordance with the responses received from the host computer system. The first partition is formatted starting at the Physical Beginning of Medium (PBOM) and may be immediately followed by the next partition or a system zone. 
     Referring to FIG. 3, there is shown the general format of a partition. The beginning of partition (BOP) 10 is a location on the tape that denotes the physical beginning of a partition. The BOP 10 is not an actual recording area on the tape but indicates the first track of the beginning of the partition. 
     The end of media warning (EMW) 16 is a recording area that contains a warning recording to be sent to the peripheral recording device when there is an attempt to record data in the area. This notifies the recording device that available recording area on the partition is about the end. 
     The end of partition (EOP) 18 is a location on the tape denoting the physical end of a partition. There is no recorded or physical marking of EOP 18 on a tape. The data track after the last data track of a partition is considered the EOP 18. Therefore, if two partitions are physically adjacent, the BOP 10 of the second partition also denotes the EOP 18 of the previous partition. 
     During the formatting of the second and later partitions, a condition may arise where a partition (P n ) will be formatted across an area of tape containing a system zone. The procedure for responding to this condition is illustrated by FIG. 4. When a new partition (P n ) is to be formatted onto the magnetic tape, the host computer system makes a determination at step 20 as to whether the formatting of P n  will cause a discontinuity in the partition. If the formatting of a partition will not cause a discontinuity, P n  is formatted onto the tape at step 22 and the recorder then returns the partitioning sequence to the step 20 to attempt to format the next partition. 
     If the formatting of P n  will cause a discontinuity in the partition, the controlling software determines at step 26 whether the host system has chosen the Pack Option, which will be discussed more fully later. If the Pack Option has been chosen, the partition is formatted across the system zones at step 28 such that the partition consists of two segments on either side of each system zone. The recording device then attempts to format the next partition and returns to step 20. 
     If the Waste or Stretch options, which will be more fully discussed later, were chosen the routine for partitioning begins a series of Partition Optimization Steps 25 designed to minimize the number of system zone interruptions for any single partition. The first step 30 divides the size of the Partition by the system zone spacing specified by the host computer system to generate a partition remainder. An inquiry 32 is then made to determine if the remainder is equal to zero. If the remainder is equal to zero, the Partition Optimization Steps 25 are completed and control will pass to step 34. 
     If the remainder generated at step 30 does not equal zero, the routine determines at step 36 if the remainder is greater than or less than the area remaining between the end of partition (EOP) 18 of the previous partition and the boundary of the next system zone. If the remainder from step 30 is less than the area remaining between the EOP 18 of the previous partition and the system zone, the Partition Optimization Steps 25 are exited and control passes to step 28 where the partition is formatted across the system zone and then seeks to format the next partition by returning to step 20. If the remainder is greater than the area remaining between EOP 18 of previous partition and the system zone, the Partition Optimization Steps 25 are exited and control passes to step 34. 
     The function of the Partition Optimization Steps 25 is to determine if the partition is to be formatted with a discontinuity despite a choice by the host computer system of the Stretch or Waste option or if the partition is to be formatted on the end-of-tape (EOT) side of the system zone. Partitions to be formatted with a discontinuity are passed through step 20 to step 28. Partitions that will be formatted on the EOT side of a system zone pass to step 34. 
     At step 34 an inquiry is made to determine if the Stretch or Waste option was chosen by the host computer system. If the Stretch option was chosen, the boundary of previous partition is expanded up to the boundary of the system zone at step 38, thus making the previous partition larger by the difference between its original boundary and the boundary of the system zone. The extended area is available for the storage of user data. The next partition is then formatted on the EOT side of the system zone at step 40. An attempt is then made to format the next partition by returning to step 26. 
     If the Waste option was chosen at step 34, the area between the previous partition and the system zone is not formatted as a result of step 42. Therefore, the area is unavailable for data storage and is wasted. The next partition is then formatted on the EOT side of the system zone at step 40 and control passes to step 26. 
     Referring to FIG. 5, there is illustrated the routine run when the last partition P n  on the tape cannot be completely formatted in the area between the EOP 18 of the previous partition and the physical end of the tape medium (PEOM). When a command is received at step 60 to format the last partition P n  that cannot be completely formatted in the remaining tape area, an inquiry 62 is made to determine if the Stretch option was chosen by the host computer system. If the Stretch option was chosen, the last partition P n  is not formatted at the end of the tape and the boundary of the previous partition is expanded at step 64 to the PEOM making this area available for data storage. The expanded partition is then declared the last partition on the volume at step 65. If the Pack or Waste option was specified, the area between the EOP 18 of the previous partition and the PEOM is not formatted (step 66) and is not available for data storage. The previous partition is then declared the last partition on the volume at step 65. 
     Under normal circumstances, the system zones will be formatted onto the tape at the spacing specified by the host computer system. However, a condition may occur near the PEOM if a requested system zone cannot be completely formatted in the area between the last partition and the physical end of the medium. The procedure for responding to this condition is illustrated in FIG. 6. 
     Referring to FIG. 6, when a command is received to format a system zone at step 80, an inquiry 82 is made to determine if the system zone can be completely formatted before the PEOM. If sufficient area is available to format the zone, the system zone is formatted at step 84 and the routine returns to inquiry 82 to format the next partition. If there is not enough space before the PEOM for another system zone, an inquiry 86 determines if another partition P n  can be formatted after the previous partition. 
     If there is a space available to format another partition on the end of the tape, another partition is formatted at step 88 and the partition is declared at step 90 the last partition on the tape. If a partition can not be formatted on the tape, an inquiry 92 is made to determine if the Stretch option was specified. 
     If the Stretch option was specified, the boundary of the last partition is extended at step 94 to the PEOM, and the partition is declared at step 90 the last partition on the tape. If the Pack or Waste option was specified, the final area of tape is not formatted (step 96) and is not available for data storage. The previously formatted partition is then declared the final partition on the tape at step 90. 
     Referring to FIGS. 7A-7C, there is illustrated the three different option formats for formatting when discontinuities in partitions may occur. When the Pack Option is chosen by the host computer system, the partition 100 is formatted on both sides of the system zone 102 such that the partition consists of two segments 104 and 106. When a Stretch Option is used, the EOP boundary 108 of the last formatted partition 110 is extended to the boundary 112 of the system zone 114. The next partition 116 is then formatted immediately after the system zone 114. This format increases the storage area of the partition 110 by the expanded area 118. Finally, when the Waste option is chosen and a partition discontinuity occurs, the next partition 120 is formatted on the EOT side of the system zone 122. The area 124 between the last formatted partition 126 and the system zone 122 is left unformatted and is not available for user data storage. 
     Data can be stored on the tape whether or not the tape has been formatted. The following description assumes the tape has bee formatted. Once a magnetic tape has been formatted by the peripheral recording device, the tape is ready to accept data storage within the formatted partitions. FIG. 8 demonstrates a prior art tape format by which data is normally stored in longitudinal tracks. Data is stored in discrete units known as physical data blocks 140. A single physical data block or a plurality of physical data blocks in a grouping are referred to as a file section 142. A file mark 148 is used to indicate the separation between two adjacent file sections 142. The file mark 148 requires the use of the storage space of an entire physical data block 140. 
     Referring to FIG. 9, there is shown the use of helical track recording with the transparent file marks of the present invention. Referring to FIG. 10, there is shown a grouping of file sections directly adjacent to each other using transparent file marks. The ending of file section 150 and the beginning of the next file section 151 are identified by storing a file section number (FSN) 152 and a data block number (DBN) 154 in the control information header 156 of each helical track 158. It is noted that while the headers 156 are shown at the beginning of each helical track 158, the headers 156 may also be interleaved within the helical track 158. In addition the file section number (FSN) 152 and the data block number (DBN) 154 are also stored in the control information header 160 (see FIG. 9) of two longitudinal tracks 161. 
     When the host computer system requests the peripheral recording device to record a file mark, the file section number 152 is incremented by one and the data block number 154 is set to zero and the numbers recorded in the control information headers 156 and the control information headers 160. The process is controlled by the peripheral recording device during the write procedures. 
     During the read procedures, the controlling software instructs the peripheral recording device to scan the FSN 152 and DBN 154 in the control information header 156 of each helical track 158 and the control information header of each longitudinal track 161 on the magnetic tape. When the recording device detects the incrementation of the FSN 52 and a zero value for the DBN 154, the recording device recognizes these values as an indication of a file mark and consequently a new file. Thus, the need for recording a file mark over an entire physical data block is eliminated. 
     If the tape has not been formatted, as long as there is a partition as shown in FIG. 3, the method proceeds in the same manner as if the tape were formatted. 
     Although preferred embodiments of the invention have been illustrated in the accompanying drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements and modifications of parts and elements without departing from the spirit of the invention.