Adaptive compression caching for tape recording
First Claim
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1. A tape drive connected to a host computer for storing and reading back user data records, said tape drive comprising:
- a tape for recording said user data records, said tape being mechanically moved whenever at least one user data record is being written to said tape and whenever at least one user data record is being read back from said tape,an electronic interface for connection to said host computer via an interface path structure,an electromechanical tape transport mechanism for transporting said tape past a read/write head structure,a data compressor in a path between said interface and said tape for selectively compressing and decompressing said user data records,an electronic cache buffer in the path between said interface and said tape for temporarily storing said user data records, andelectronic control means responsive to a data record level of said cache buffer for selectively enabling and disabling said data compressor to maintain a desired data record level in said cache buffer in order to maximize a data transfer rate between said host computer and said tape.
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Abstract
A method selectively compresses data entering a data storage device, such as a digital linear tape drive, based upon whether a data level of a device cache buffer is above a predetermined watermark reference level. If the data level is above the predetermined reference, a data record entering the storage device bypasses a data compressor on its way to storage. After each record is transferred the buffer level is redetermined. When the buffer level falls below the watermark, the data compressor is reenabled and a subsequent data record is compressed before being stored.
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Citations
28 Claims
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1. A tape drive connected to a host computer for storing and reading back user data records, said tape drive comprising:
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a tape for recording said user data records, said tape being mechanically moved whenever at least one user data record is being written to said tape and whenever at least one user data record is being read back from said tape, an electronic interface for connection to said host computer via an interface path structure, an electromechanical tape transport mechanism for transporting said tape past a read/write head structure, a data compressor in a path between said interface and said tape for selectively compressing and decompressing said user data records, an electronic cache buffer in the path between said interface and said tape for temporarily storing said user data records, and electronic control means responsive to a data record level of said cache buffer for selectively enabling and disabling said data compressor to maintain a desired data record level in said cache buffer in order to maximize a data transfer rate between said host computer and said tape. - View Dependent Claims (2, 3, 4, 5)
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6. A tape drive connected to a host computer for storing and reading back user data records, said tape drive comprising:
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a tape for recording said user data records, said tape being mechanically moved whenever at least one user data record is being written to said tape and whenever at least one user data record is being read back from said tape, an electronic interface for connection to said host computer via an interface path structure, an electromechanical tape transport mechanism for transporting said tape past a read/write head structure, a data compressor in a path between said interface and said tape for selectively compressing and decompressing said user data records, an electronic cache buffer in the path between said interface and said tape for temporarily storing said user data records, and electronic control means responsive to a data record level of said cache buffer for selectively enabling and disabling said data compressor to maintain a desired data record level in said cache buffer in order to minimize a number of start and stop operations of the electromechanical tape transport mechanism. - View Dependent Claims (7, 8, 9, 10)
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11. A method for selectively compressing data entering a data storage device, the device including a data compressor, a bypass path selectively enabled around the data compressor, a cache buffer, and a storage medium connected to receive data from the cache buffer, the method comprising the steps of:
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receiving a plurality of data records of predetermined size from a host computer connected to the data storage device, compressing at least one of the plurality of data records by passing the record through the data compressor and then into the cache buffer, determining if a data level of the cache buffer following receipt of the at least one of the plurality of data records is above a predetermined watermark reference, and if so, enabling the bypass path around the data compressor, transferring an uncompressed next one of the plurality of data records around the data compressor and into the cache buffer, redetermining the data level of the cache buffer following transfer of the uncompressed next one of the plurality of data records, selectively disabling the bypass path depending upon the redetermined data level of the cache buffer, and transferring the data in the cache buffer to the storage medium. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A tape drive connected to a host computer for storing and reading back user data records, said tape drive comprising:
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a tape for recording said user data records, an electromechanical tape transport mechanism for transporting said tape past a read/write head structure, said tape being mechanically moved whenever at least one user data record is being written to said tape and whenever at least one user data record is being read back from said tape, an electronic interface for connection to said host computer via an interface path structure, an electronic cache buffer connected to a data path to and from the read/write head structure, for temporarily storing said user data records, the electronic cache buffer having a first input port and a second input port, a data compressor in a path between said interface and the first input port for selectively compressing and decompressing said user data records, an incoming control point in the path between said interface and said electronic cache buffer for selectively connecting a data compressor bypass path from the electronic interface to the second input port, a record buffer between the incoming control point and the data compressor, and electronic control means responsive to a data record level of said electronic cache buffer for controlling the incoming control point to selectively pass records through the record buffer and data compressor and through the bypass path around said record buffer and data compressor so as to maintain a desired data record level in said cache buffer. - View Dependent Claims (25, 26)
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27. A tape drive connected to a user data record source for storing and reading back user data records, said tape drive comprising:
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a tape for recording said user data records sent by the user data record source, said tape being mechanically moved whenever at least one user data record is being written to said tape and whenever at least one user data record is being read back from said tape, an electronic interface for connection to said user data record source via an interface path structure for receiving a sequence of user data records to be recorded to said tape, an electromechanical tape transport mechanism for transporting said tape past a read/write head structure, a data compressor in a path between said interface and said tape for selectively compressing and decompressing ones of said user data records, an electronic cache buffer in the path between said interface and said tape for temporarily storing said user data records, and electronic control means responsive to a recurrent cache buffer level determination for selectively enabling and disabling said data compressor to maintain a data record level in said electronic cache buffer as will cause at least one of; maximizing a transfer rate of the sequence of user data records from said user data record source to said tape, and minimizing a number of start and stop operations of the electromechanical tape transport mechanism during recording of the sequence of user data records. - View Dependent Claims (28)
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Specification