MAGNETIC TAPE SYSTEM WITH WRITE RETRY MEANS

Abstract: A magnetic tape system wherein when a write error is caused by writing data on a magnetic tape (16) by a magnetic head (14), the write error is processed according to a variable length erase method. In this magnetic tape system, when a write error occurs, a write retry operation is executed, an lengths of blocks (IBG1,...IBGn) erased by the write retry oper­ ation are integrated. When the integrated length (L) exceeds a predetermined value (LR), a tape error is reported, and forma­ tion of a long IBG having a length (L) exceeding the length (LR) specified by the ISO standard is prevented.

Description: The present invention relates to a magnetic tape system. More particularly, the present invention relates to a magnetic tape system in which write retry is automatically executed when a write error occurs. A magnetic tape system is widely used as an external memory device of an electronic computer. Recently, this magnetic tape system has been utilized for the backup operation of other memory devices, such as a magnetic disc device, having a short access time. In such a magnetic tape system, writing is effected in individual blocks and an interblock gap (IBG) is formed between every two adjacent blocks to separate each block. In this magnetic tape system, if a write error occurs while the data of one block is being written, the written block is erased and re-writing, that is, write retry, is executed. If write retry is limited only by the number of retries, however, in a so-called variable length block system where the erase block length is not constant, a problem arises of magnetic tape incompatibility. This problem will be described in detail hereinafter. CH-A-572 261 discloses a magnetic tape system in accordance with the preamble of accompanying claim 1. An embodiment of the present invention may provide a magnetic tape system in which write retry is executed according to a variable length erase method, wherein an excess of the IBG length by write retry beyond a predetermined value is prevented and a compatible tape can be provided. More specifically, in accordance with one aspect of the present invention, there is provided a magnetic tape system including a driving unit including a magnetic head, reels having a magnetic tape wound thereon and a drive portion for driving the reels, a drive control unit operatively connected to the drive unit to control the drive unit, and a command and data control unit operatively connected to the drive control unit and a host controller for transmitting access commands to the magnetic tape to actuate the drive unit through the drive control unit according to the commands transmitted from the host controller and to transmit the results of the operation to the host controller. The command and data control unit writes data of one block in the magnetic tape according to write commands and data from the host controller and detects the occurrence of an error in the write operation, and if an error occurs, the written block is erased and the data from the host controller is rewritten in a block subsequent to the erased block. The command and data control unit adds the length of blocks erased by rewriting, and if the erased block length in the magnetic tape exceeds a predetermined value, the above-mentioned rewriting operation is stopped. Furthermore, the command and data control unit may transmit an error signal to the host controller when the length of blocks erased by rewriting exceeds a predetermined value. Moreover, the command and data control unit may hold write data when the length of blocks erased by rewriting exceeds a predetermined value. Still further, the command and data control unit may carry out a rewriting operation at an erased block length determined according to the write density of the magnetic tape. A second aspect of the present invention is as set forth in claim 7. Reference is made, by way of example, to the accompanying drawings in which: Figs. 1a through 1e are diagrams illustrating a write retry operation ; Fig. 2 is a schematic view illustrating a magnetic tape system according to one embodiment of the present invention; Fig. 3 is a schematic view illustrating a command and data control unit in the embodiment shown in Fig. 2; Figs. 4 and 5 are flow charts illustrating write retry operations in the magnetic tape system shown in Figs. 2 and 3; and Figs. 6 and 7 are diagrams illustrating the principle of the present invention. Before explaining the preferred embodiments of the present invention, the write retry operation will be described with reference to Figs. 1a through 1e. In the following description made with reference to Figs. 1a through 1e, a magnetic head 14 is moved for the write retry operation. This, however, is only for facilitating the expression in the drawings and an understanding of the operation; in practice, a magnetic tape 16 is moved while the magnetic head 14 is fixed. Generally, the magnetic head 14 performs a read operation after data storage from the rear end of the IBG of the magnetic tape 16, as shown in Fig. 1a, checks the written data, and when at the point X in Fig. 1a it is detected that the written data is different from the read data, a write error is detected and a retry operation is executed. This retry operation will now be described. At first, as shown in Fig. 1b, the magnetic head 14 is backspaced (repositioned) to the rear end of the IBG of the magnetic tape 16. Then, as shown in Fig. 1c, the area of the corresponding one block of the magnetic tape 16 is erased by the magnetic head 14. Furthermore, as shown in Fig. 1d, the erased area is designated as IBG1, and the content of that block is written from the rear end of IBG1 by the magnetic head 14. If a write error is again detected during the write retry operation shown in Fig. 1d, the magnetic tape 14 is again backspaced to the rear end IBG1 of the magnetic tape 16, as shown in Figs. 1b through 1d, the area of the corresponding block is erased, and the writing operation is again executed from the rear end IBG2 (see Fig. 1e). In this case, erasure is just not performed on the error-occurring position on the magnetic tape 16 but on the area of one whole block of data. This is because, when erasing a fixed length (for example, erasing for 3 inches of tape), it is feared that the error-occurring position will not be erased, and therefore, the above-mentioned erasing manner is adopted to ensure that the error-occurring position is properly erased. This erasing method is called "variable length erasing" because the area to be erased depends on the length of the block. In this write retry operation, if the magnetic tape 16 is deteriorated and the write retry operation is repeated, a write error occurs and the normal writing operation is impossible. Accordingly, the number of write retry operations for data of one block is limited, and if the number of the write retry operations exceeds a certain limit, it is judged that a tape error (tape use impossible) has occurred, and the write retry operation is not again performed. On the other hand, if writing of data in one block is successful within the above-mentioned limit of the number of write retry operations and an error does not occur, termination of the normal operation is reported to a host controller. In the case of a variable length block where the block length is not constant, if the write retry operation is limited only by the number of retries, the disadvantages described below are incurred. According to the International Standards Organization (ISO) for example, the maximum length of an IBG is set as 7.6 m in the phase encoding (PE) system (1600 bits per inch) and as 4.5 m in the group coded recording (GCR) system (6250 bit per inch). In the previous technique, since the write retry operation is limited by the number of retries, in the case of a certain block length it is possible to exceed the maximum length of the IBG even if the number of write retry operations is within the limit. For example, if one block has a length of 64 kilobytes, when the writing operation is performed according to the PE system, the block length on the magnetic tape 16 is about 1 m. Accordingly, if the write retry operation is performed 8 times within the limit, the IBG exceeds the maximum length of 7.6 m. Therefore, a magnetic tape 16 having an IBG exceeding the limitation of the IBG length determined by the ISO standard or the like is prepared, but there is no guarantee that this magnetic tape having an IBG exceeding the standard can be read out by a different tape system, and a problem arises concerning the compatibility of the magnetic tape. Embodiments of the present invention will now be described. Figure 2 is a diagram of the structure of a magnetic tape system according to one embodiment of the present invention. Reference numeral 1 represents a magnetic tape drive unit (hereinafter referred to as "drive") of a direct reel-to-reel drive system, which is constructed so that a magnetic tape 16 travels between a take-up reel (machine reel) 11 and a feed reel (file reel) 12 and is wound on the take-up reel 11 through a roller 15a of a tension arm 15, a magnetic head 14, and an idler 13. The magnetic tape 16 is guided by guides 17a and 17b on both sides of the magnetic head 14. The take-up reel 11 and the feed reel 12 are rotated and driven by drive motors 10a and 10b, respectively. Rotary encoders 18 and 18b are mounted on the drive motors 10a and 10b to detect the number of rotations of the drive motors 10a and 10b. A rotary encoder 19a is mounted on the idler 13 to make it possible to determine the actual travelling position of the tape, and a tension detector 19b is mounted on the tension arm 15 to enable detection of the tape tension. Reference numeral 2 represents a drive controller for driving and travelling the tape and driving the head for writing or reading according to commands and data transmitted from a command and data controller described hereinafter. The drive controller 2 receives outputs from the respective rotary encoders 18a, 18b and 19a to determine the state of travel of the tape and receives the output from the tension detector 19b to check the tension of the tape. Furthermore, the drive controller 2 controls both the drive motors 10a and 10b through drive circuits 20 and 21. Thus, the drive controller 2 drives and travels the tape under a constant tape tension, transmits data to be written to the magnetic head 14 to effect writing and receives data read by the magnetic head 14. Reference numeral 3 represents a command and data controller which receives write commands or read commands from the host controller and accumulates written data therein. In the case of a write command, the command and data controller 3 transmits a write command and data to be written to the drive controller 2 to effect the writing operation, and if the operation is normally terminated, the command and data controller 3 informs the host controller of this normal termination. If the operation is not normally terminated, the command and data controller 3 causes the drive controller 2 to effect the write retry operation. Note, the control means is comprised of the command and data controller 3 and the drive controller 2, and the command and data controller 3 acts as a magnetic tape device to the host controller and as a host controller to the drive controller 2. Figure 3 is a diagram illustrating the command and data controller 3 in the system shown in Fig. 2. In Fig. 3, reference numeral 30 represents a micro-processor (hereinafter referred to as "MPU"), which performs control of the receipt of commands and data from the host controller and control of the transmission of data and status according to a micro-program of a program memory, and also performs control of the transmission of commands and data to the drive controller 2 and control of the receipt of data and status from the drive controller 2. Moreover, the micro-processor 30 performs the processing of a retry control. Reference numeral 31a represents a program memory in which programs to be executed by the MPU 30 are stored. Reference numeral 31b represents a random access memory (hereinafter referred to as "RAM"), in which data, commands, and parameters necessary for the MPU 30 processing are stored. In this embodiment, the RAM 31b has a retry count area RC for writing the number of retry operations and an IBG count area IC for writing the IBG length. Reference numeral 32a represents a drive interface circuit for the transfer of control signals and the like between the drive controller 2 and the command and data controller 3. Reference numeral 32b represents a host interface circuit for the transfer of control signals and the like between the host controller and the command and data controller 3. Reference numeral 33 represents a data transfer control circuit for controlling a data buffer, described hereinafter, to control the transfer of data between the host controller or the drive controller 2 and the command and data controller 3. The control circuit 33 transmits a data transfer demand signal to the host controller and receives a data transfer demand signal from the drive controller 2 to execute control of the data transfer. Reference numeral 34 represents a data buffer controlled by the data transfer control circuit 33. The data buffer 34 stores the data to be stored from the host controller and transfers the stored data to the drive controller 2. The buffer 34 also stores the data read from the drive controller 2 and transfers the read data to the host controller. The data buffer 34 has, for example, a capacity of 256 kilobytes. Reference numeral 35 represents a data bus for connecting the MPU 30 to the program memory 31a, RAM 31b, drive interface circuit 32a, host interface circuit 32b, and data transfer control circuit 33 to execute the transfer of commands and data. Reference numeral 36a represents a control signal line used to transmit commands to the drive controller 2 and receive status and the like from the drive controller 2. Reference numeral 36b represents a line for a signal showing a detection of a region adjacent to the tape end, which is used for transmitting this signal from the drive controller 2. Reference numeral 36c represents an interruption line which is used for informing the MPU 30 of an interruption from the drive interface circuit 32a. Reference numeral 37a represents a data transfer demand signal line for transmitting a data transfer demand signal to the data transfer control circuit 33 from the drive controller 2. Reference numeral 37b represents a store data bus used for transmitting the stored data to the drive controller 2 from the data buffer 34. Reference numeral 37c represents a read data bus used for transmitting the read data to the data buffer 34 from the drive controller 2. Reference numeral 38 represents a control signal line used for the transfer of commands and status between the host controller and the command and data controller 3. Reference numeral 39a represents a data transfer demand signal line used for transmitting a data transfer demand signal to the host controller. Reference numeral 39b represents a store data bus used for transmitting the stored data from the host controller to the data buffer 34. Reference numeral 39c represents a read data bus used for transmitting the read data to the host controller from the data buffer 34. Accordingly, the MPU 30 executes storing and reading among RAM 31b, the host interface circuit 32b, the drive interface circuit 32a, and the data transfer control circuit 33 through the data bus 35 to perform the desired processing. More specifically, the host interface circuit 32b performs the transfer of commands and status by the control of the MPU 30 through the host controller and the control signal line 38, and the drive interface circuit 32a performs the transfer of commands and status by the control of the MPU 30 through the drive controller 2 and the control signal line 36a. According to the instructions from the MPU 30, the data transfer control circuit 33 transmits a data transfer demand to the host controller through the data transfer demand signal line 39a, and on receipt of this signal, the host controller transmits the stored data to the data buffer 34 through the store data bus 39b and the stored data is accumulated in the data buffer 34. The data transfer demand transmitted through the data transfer demand signal line 37a from the drive controller 2 causes the data transfer control circuit 33 to transmit the stored data of the data buffer 34 to the drive controller 2 through the stored data bus 37b. Furthermore, the instructions from the MPU 30, cause the data transfer control circuit 33 to accumulate the read data transmitted from the drive controller 2 through the read data bus 37c in the data buffer 34 and to transmit the read data of the data buffer 34 to the host controller through the read data bus 39c. Figure 4 is a flow chart illustrating the processing in one embodiment of the present invention. Before the explanation of Fig. 4, the operation of receiving commands and data from the host controller is first described. The command (writing or reading) from the host controller is given to the host interface circuit 32b through the control signal line 38, the MPU 30 reads out the command through the data bus 35 and recognizes the content of the command, and the recognized command is stored in the command store area. If the command is a write command, MPU 30 transmits a write address to the data transfer control circuit 33 and a data transfer demand is transmitted to the host controller from the data transfer demand signal line 39a. The MPU 30 receives the data to be written from the host controller through the stored data bus 39b, and the data to be written is stored in the instructed store address of the data buffer 34. When the MPU 30 receives the termination report from the drive controller 2, the MPU 30 analyzes the command stored in the command store area of the RAM 31b, and if the command is a write command, processing of the write command is performed according to the routine shown in Fig. 4, which is explained as follows. Step S011 The MPU 30 clears the IBG count area Ic and retry count area RC of the RAM 31b to zero. Step S012 The write command is transmitted to the drive controller 2 through the drive interface circuit 32a and the control signal line 36 to actuate the drive controller 2, and a response signal (data busy) from the drive controller 2 is received through the drive interface circuit 32a to start an automatic transfer. More specifically, the MPU 30 transmits the address of the written data corresponding to the write command in the data buffer 34 as the load address, and the byte number of the written data corresponding to the write command as the load byte count value, to the data transfer control circuit 33 to prepare for an automatic transfer. On receipt of the data transfer demand signal from the drive controller 2, the data transfer control circuit 33 sends the written data to the drive controller 2 from the data buffer 34 through the store data bus 37b, whereby the drive controller 2 starts the travelling of the magnetic tape 16 and the writing of the data written on the magnetic tape 16 is performed by the magnetic head 14 while the written content is also read out by the magnetic head 14 to accomplish the read-after-write checking. If execution of the write command by the drive controller 2 is normally terminated, a normal termination report is sent to the MPU 30 from the control signal line 36a through the drive interface circuit 32a, but if an error has occurred, an abnormal report is similarly sent to MPU 30. Step S013 The MPU 30 analyzes the content of the information received, and in the case of a normal termination, the routine goes to a termination report routine and the corresponding write command of the command write area of RAM 31b and the write data of the data buffer are invalidated and a normal termination report is sent to the host controller through the host interface circuit 32b. Step S014 In the case of an abnormal report, the MPU 30 transmits a sense command to the drive controller 2 through the drive interface circuit 32a and determines the content (nature) of the abnormality (error) of the drive controller 2. In response to this inquiry, the drive controller 2 informs the drive interface circuit 32a of the content of the error through the control signal line 36a. Step S015 The MPU 30 analyzes the content of the error, and if the error is a system error (impossible to block write or read or improper travelling speed of the tape), the routine goes immediately to an error information forming routine and the operation is stopped, and the termination because of an abnormality is reported to the host controller through the host interface circuit 32b, On the other hand, if the error is a write error (data check error), the MPU 30 checks the content of the retry count area RC of the RAM 31b, and a check is made to determine whether the number of retries has exceeded the predetermined value (excessive retry). In case of an excessive retry, as in the above-mentioned case of a system error, the routine goes to the error information forming routine, the operation is stopped, and termination of the abnormality is reported to the host controller. Steps S017 through S020 If the number of retries does not exceed the predetermined value (not excessive retry), the MPU 30 determines whether the set write density is 1600 bpi or 6250 bpi, and the block length (byte number, LBLK₁ or LBLK₂) of the write data, which differs according to the write density, is added to the content of the IBG length area IC of the RAM 31b to renew the content of the IBG length area IC. If the write density is for example 1600 bpi, it is determined whether the content of the IBG length area IC exceeds the length limit (e.g. 6 m), and if the write density is for example 6250 bpi, it is determined whether or not the content of the IBG length area IC exceeds the length limit (e.g. 3.6 m). The limit length is shorter than the maximum length specified by ISO or other Standard because errors in the travelling speed of the tape are taken into consideration. If the content of the IBG length area IC exceeds the length limit, the routine goes to the error information forming routine, the operation is stopped, and termination of the abnormality is reported to the host controller. Steps S022 through S024 If the content of the IBG length area IC does not exceed the limit length, the retry operation is allowed. At first, 1 is added to the content of the retry count area RC of RAM 31b to renew the content of the retry count area RC. Then, the MPU 30 transmits a backspace command to the drive controller 2 from the drive interface circuit 32a through the control signal line 36a, and the drive controller 2 then feeds the magnetic tape 16 backward and backspaces the tape 16 as shown in Fig. 1b. Furthermore, the MPU 30 transmits a variable length erase command VLEC to the drive controller 2 from the drive interface circuit 32a through the control signal line 36a. By this command VLEC, the drive controller 2 is caused to feed the magnetic tape 16 block by block in the normal direction, as shown in Fig. 1c, and to drive the magnetic head 14 to effect the erasing operation. Note, prior to transmission of the variable length erase command VLEC, as in the case of the write command, the byte count value is transmitted to the data transfer control circuit 33 to prepare for an automatic transfer. The variable length erase command is accompanied by a data transfer operation as well as the write command, but the written data has no particular significance. The routine then returns to step S012, and the MPU 30 again executes the writing operation. If the write retry operation is thus executed and the number of retries exceeds the limit, the operation is stopped (excessive retry). Even if the number of retries is within the limited value, if the erase block length (IBG length) exceeds the length limit, this is judged to be a tape error (tape abnormality) and the operation is stopped. In the present embodiment, before erasing, the block length to be eliminated is added to the IBG length, and the IBG length is then determined. Accordingly, the write error-occurring block is left on the tape 16 and is used for subsequent analysis of the error. Moreover, an unnecessary retry operation need not be performed. Figure 5, is a flow chart of the processing in another embodiment of the present invention. In this embodiment, the order of steps S013 through S016 and S017 through S021 in Fig. 4 is changed to steps S031 through S035 and S036 through S039, and after execution of the write command at step S012, steps S031 through S035 for determining the IBG length are inserted. In this embodiment, the actual erase length is added to the IBG length and the value obtained thereby is subjected to a determination. Also, in this embodiment, the written data is left on the tape 16 and is used for subsequent analysis of the error. The principle of the present invention adopted in the foregoing embodiments will now be described with reference to Figs. 6 and 7. Upon writing one block, as shown in Fig. 6, the erase length ℓ1 by the write retry is integrated at every write retry to obtain an integrated value L. As shown in Fig. 7, the erase block length L is compared with the predetermined length LR, and if the erase block length L exceeds the predetermined length LR, it is judged that a tape error has occurred and a further retry is inhibited. As is apparent from the foregoing description, according to the present invention, lengths of erased blocks are integrated and it is determined whether or not the integrated value exceeds the predetermined length. Accordingly, the formation of a magnetic tape having a write content in which the IBG length exceeds the standard value may be prevented, tape compatibility may be maintained, and writing outside the range specified by the ISO standard may be prevented. Moreover, the present invention can be easily realized, and the present invention provides excellent practical effects. It should be understood that the present invention is not limited to the specific embodiments described in this specification, except as defined in the appended claims. Especially, the present invention is not limited to ensuring compatability with ISO Standards or to recording by phase encoding (PE) and group coded recording (GCR) systems.

Claims: A magnetic tape system comprising: drive means (1) for a magnetic tape (16); drive control means (2, 20, 21) operatively connected to said drive means to control said drive means; and command and data control means (3) operatively connected to said drive control means and a host controller (5) for feeding access instructions to said magnetic tape to operate said drive means through said drive control means; wherein said command and data control means (3) is constructed so'that in operation, said command and data control means writes data of one block on said magnetic tape (16) according to write commands and data from said host controller (5) and when an error caused by said writing operation is detected, a written block is erased and data from said host controller (5) is re-written in a block subsequent to said erased block; characterised by the means for adding lengths of blocks erased by re-writing and means for stopping said re-writing when an erase block length of said magnetic tape (16) exceeds a predetermined value. A magnetic tape system as set forth in claim 1, wherein when the erase block length of said magnetic tape (16) exceeds a predetermined value, an error signal is transmitted to said host controller (5). A magnetic tape system as set forth in claim 1 or 2, wherein when the erase block length of said magnetic tape (16) exceeds the predetermined value, the written data is maintained. A magnetic tape system as set forth in claim 1,2 or 3, wherein the erase block length of said magnetic tape (16) is determined according to a write density of said magnetic tape. A magnetic tape system as claimed in any preceding claim, wherein said drive means (1) includes a magnetic head (14), reels (11,12) for winding the magnetic tape (16) thereon, and a drive portion for driving said reels. A magnetic tape system as claimed in any preceding claim, wherein said command and data control means (3) is operable according to instructions from said host controller (5) to operate said drive means (1) through said drive control means (2,20,21) and is operable to report results of said operation to said host controller (5). A method of performing a write retry operation in a magnetic tape system, comprising steps of, repeatedly but not necessarily in this order: a) erasing a portion of the magnetic tape (16) to remove a block of data in which a write error has occurred; b) rewriting the block of data onto an adjacent portion of the magnetic tape; c) determining whether the written block of data contains an error and if it does not, terminating the write retry operation; and d) adding the length (1) of the portion of the magnetic tape erased in the preceding erasing step a) to a stored value (L) representing the length of an inter-block gap and comparing the result to a predetermined length value (LR), and if the result exceeds the predetermined length value, terminating the write retry operation. A method of performing a write retry operation as claimed in claim 7, comprising the further step of: incrementing a stored value representing a number of times of performing the rewriting step b), and comparing the stored value with a predetermined number, and if the stored value exceeds the predetermined number, terminating the write retry operation.

Inventors: ISHIGURO, MASAYUKI, OWA, NOBORU
Applicants: FUJITSU LIMITED
Application year: 1986
Main classification: G11B20
IPC codes: G11B20, G11B5