Abstract: An error tolerant detection of multibit synchronization characters within data blocks in a data storage system. Each detected prospective multibit synchronization character is compared to an expected multibit synchronization character for an identical match and for a match which includes a variation of no greater than two adjacent bits. A synchronization character is then considered to be identified in response to a successful exact comparison or, if relaxed detection is enabled, in response to a successful comparison indicating that the detected prospective multibit synchronization character does not differ from the expected multibit synchronization character by an error greater than two adjacent bits. For Read While Write operation in which it is imperative that the synchronization characters be written initially without error, the relaxed detection scheme may be selectively disabled, requiring the synchronization characters to achieve an exact match with the expected synchronization character.

Abstract: A method and apparatus for accurately locating targeted append points in a tape drive. The effects of interlayer slip (ILS) are eliminated and smaller IBGs are possible thus providing increased data capacity for a given tape cartridge. A coarse tachometer count is used in combination with the read dataflow to accurately locate the proper append point even with a small IBG size. The appended data are assured to be written using the proper tape velocity which virtually eliminates improper write appends and read temporary errors previously caused by ILS effects. The solution also guarantees that customer data previously written to the tape are not accidentally overwritten.

Abstract: A method and apparatus which first calculates track to track skew in a tape device and then uses the results of that calculation to adjust the windows for detection of sync and resync characters. The system makes use of global circuitry which adjusts the sync and resync windows for all tracks based upon the skew calculation. In the case of the windows used for detecting resyncs, when skew is determined to be large, the global resync window must span a larger time period to account for the skew in detecting resync marks. Conversely, when there is little or no skew present, the windows for resync detection can be narrowed. Normally, the track logic utilizes its own local windows to detect resyncs. If a track misses a resync, however, it must use the global resync window to determine the next resync location. Once the tracks are resynchronized, control can return to local track circuitry to maintain synchronization.

Abstract: An apparatus and method for detecting and validating formatted blocks during read/write data operations in a magnetic tape data storage system includes component functionality for reading and writing data on a magnetic tape medium in a plurality of modes, including a read-only (R) mode and a read-while-write (RWW) mode, the data being arranged in one or more tracks in a sequence of formatted blocks. In preferred embodiments, formatted block detection and validation is performed by appropriate logic circuitry configured to detect at least one formatting entity representing an inter-block gap, a block acquisition burst, a synchronization character, or any other desired formatting entity, using first and second programmable detection thresholds that are the same or substantially the same in both the R and RWW modes.

Abstract: A tape drive data storage apparatus incorporates a system for dynamically anticipating and resolving potential data error conditions. The system performs read and/or write data transfer operations on a tape medium, during which time it generates a track performance database representing a map of potential data error conditions occurring on the tape. As operations continue, determination is made from the track performance database whether one or more track fallout thresholds have been reached in one or more regions of the tape. If so, an error recovery bellcord action is performed to minimize the occurrence of data error conditions.

Abstract: A method and system for accurately reading and storing data as multiple data blocks on a removable data storage medium mounted within a data storage system. Each data block includes an initial acquisition data character and multiple diverse synchronization characters/bursts and adjacent data blocks are separated by a unique interblock gap character. A multimodal interblock gap character detection circuit is provided which may operate in a normal mode of operation or a stringent mode of operation, wherein an enhanced degree of certainty is required for detection of the interblock gap character. A predicted time window of occurrence for a next interblock gap character is generated in response to detection of an initial acquisition data character and at least one synchronization character within a data block. Additionally, a global clock count signal based upon multiple track outputs is generated each time a resynchronization burst is encountered.

Abstract: A data storage system has error detecting and correcting system having three error codes. The data are arranged logically as a three-dimensional array consisting of a plurality of logically rectangular blocks of data. Each block of data has columns and rows of data. A first error code that corrects errors creates a first redundancy in each of the columns. A like-positioned block row of data in each of the blocks constitutes an array row of data. The array rows are grouped into sets of array rows, the number of array rows in each set vary inversely with a number of tracks of a record medium that concurrently receive the data for recording. Each set of data are recorded serially by bit in respective tracks of the tape record medium. Before recording, the block rows are logically rotated (end-around shifted) within each of the array rows.

Abstract: A method and system for detecting and validating multibit acquisition burst sequences which precede and follow each data block in a multitrack data storage system. An acquisition sequence pattern detection circuit is utilized to provide an indication of acquisition burst sequence detection in response to an occurrence of an accurate sequence of a selected number of acquisition burst sequence bits. A latch is utilized to store the pattern criteria indication for each associated track and the latch outputs are then combined in a logic circuit to provide a composite burst pattern error indication signal.

Abstract: A method and apparatus which first calculates track to track skew in a tape device and then uses the results of that calculation to adjust the windows for detection of sync and resync characters. The system makes use of global circuitry which adjusts the sync and resync windows for all tracks based upon the skew calculation. In the case of the windows used for detecting resyncs, when skew is determined to be large, the global resync window must span a larger time period to account for the skew in detecting resync marks. Conversely, when there is little or no skew present, the windows for resync detection can be narrowed. Normally, the track logic utilizes its own local windows to detect resyncs. If a track misses a resync, however, it must use the global resync window to determined the next resync location. Once the tracks are resynchronized, control can return to local track circuitry to maintain synchronization.

Abstract: A tape drive data storage apparatus incorporates an error recovery system that is dynamically controlled to perform knowledge-based error recovery in accordance with a novel error recovery method. As the tape drive apparatus performs read and/or write data transfer operations on a tape medium loaded in the tape drive, an error recovery knowledge base is generated representing a tape map of ECC error correction locations on the tape medium. If error recovery is initiated and it is determined from the tape map that one or more error clustering thresholds have been reached in one or more selected regions of the tape medium, appropriate error recovery action is taken depending on whether a data read or data write operation is underway. If read (or write) data is being processed, the error recovery procedures performed by the error recovery system can be selectively modified in the affected tape medium regions to address the expected cause(s) of the data error.