1. Field of the Invention
The present invention relates to an apparatus and a method for controlling transportation of a tape medium. In particular, the present invention relates to an apparatus and a method for controlling transportation of a tape medium during data writing to the tape medium.
2. Description of the Related Art
During data writing, some tape drives write data to tape media, such as magnetic tapes, in conformity with LTO (Linear Tape Open), for example, by receiving synchronization commands from a host (an application program) at regular or sporadic time intervals. The synchronization command is a command to forcedly write data accumulated in a buffer in a tape drive to a tape medium. Such regular reception of synchronization commands assures an application program that all data sent to the tape drive by the application program itself is already written to the tape medium and is not left any more in the buffer in the tape drive.
When the tape drive receives a synchronization command, the buffer inside the tape drive becomes empty, and the tape medium is transported idly without data to be written. In order to keep an interval between recorded datasets, the tape drive usually performs “backhitch.” The backhitch is a series of operations including stopping the transportation of the tape medium once by reducing the transport speed of the tape medium, transporting the tape medium in a reversed direction, thereafter transporting the tape medium again in the original direction until a location of the tape medium targeted for writing arrives, and then writing next data to the location. This backhitch usually requires a time of approximately two or three seconds. Since the writing of next data starts after completion of this backhitch, frequent reception of synchronization commands leads to considerable reduction in writing performance.
To address this, there have been heretofore proposed techniques of writing without execution of backhitch (for example, see Japanese Patent Application Publication Nos. 2006-318571, 2004-341925, 2008-533636).
Japanese Patent Application Publication No. 2006-318571 describes an apparatus including a host I/F unit to store a dataset sent from a host into a buffer memory, as well as to take out a dataset stored in the buffer memory and to send the dataset to the host, and a medium I/F unit to take out a dataset stored in the buffer memory and to transfer the dataset to a tape, as well as to store a dataset read from a tape into the buffer memory. The apparatus acquires a transfer rate with the host from the host I/F unit, acquires an error rate in writing to the tape from the medium I/F, determines a tape speed based on the transfer rate and the error rate, and performs control to transport the tape with the determined speed.
Japanese Patent Application Publication No. 2004-341925 describes a storage apparatus to sequentially write multiple sets of write data to a data recording medium in segment units of a predetermined size. For each of sets of write data, the storage apparatus writes the set of write data to at least one segment of the data recording medium when the set of write data is received in association with a write command to write the set of write data to the data recording medium. In the case where the size of one set of write data is smaller than a prescribed size that is determined in advance, the storage apparatus concatenates the one set of write data and multiple sets of write data written after the one set of write data, among the multiple sets of write data sequentially written to the data recording medium, and then writes the concatenated sets of write data to a smaller number of segments than the number of segments originally required to write the sets of write data targeted for the concatenation. In addition, according to Japanese Patent Application Publication No. 2004-341925, the storage apparatus performs backhitchless flush of writing write data to a tape recording medium without executing backhitch, and thereby operates with a higher speed than in the case of executing the backhitch.
Japanese Application Publication No. 2008-533636 describes a helical scan tape recorder including a rotatable scanner, and a transport system for transporting a magnetic tape to a position proximate to the rotatable scanner in such a manner that information can be recorded during a revolution of the scanner. In the helical scan tape recorder, a controller performs, as a pause routine for pausing during a recording operation on the tape, the steps of: determining a tape pause position reference value indicative of a pre-pause last recording position on the tape; recording an erase signal on the tape after the pre-pause last recording position; rewinding the tape; transporting the tape in a forward direction and obtaining a current tape position value; determining when the current tape position value reaches a predetermined value relative to the tape pause position reference value; and at beginning of a next revolution of the scanner, commencing recording of one or more post-pause stripes on the tape.
One conceivable method of backhitchless writing is to idly transport a tape (transport the tape without writing data) after receiving a synchronization command until next data is ready to be written. However, since a time to write data to the tape is proportional to a tape speed, there is a case where a high tape speed is used to reduce the write time. The use of the high tape speed leads to an increase in the idly-transported length, and thereby causes a problem of lowering the performance in reading.
In contrast, in order to achieve a target value of the performance in reading, there is no way but to make the idly-transported length short, and the backhitch is executed for this purpose. Therefore, a time of entire write processing cannot be reduced in consideration of an occurrence frequency of backhitch and a time required for backhitch.