Method for utilizing a longitudinal track on a helical scan tape data storage system to provide a fast search capability
First Claim
1. In a data recording system using magnetic tape for storing data, said recording system connected to a host computer, said recording system using a recording format on said magnetic tape employing a plurality of helically scanned tracks for storing said data, including a first longitudinal track for storing magnetic tape position information indicative of location of said data and a second longitudinal track containing position marks and servo control pulses, said position information being written at equally spaced predetermined locations on a said first longitudinal track, said position information comprising a plurality of file marks and sector marks said data being logically segmented into files containing sectors comprising data blocks, and wherein said data recording system uses a tape drive control unit to store a memory copy of said header area from said magnetic tape, a method for locating a selected block in response to a command from said host computer, said command including indicia of location of said selected data block comprising the steps of:
- placing a header area on said helically scanned tracks for locating said selected block, said header area containing indicia of location of said data blocks comprising the number of said servo control pulses between said header area and a location of each of said blocks;
reading said memory copy of said header area to determine whether valid magnetic tape position information is contained therein; and
employing redundant strategies for locating said selected data block, one of said strategies being selected according to a data integrity of said header area, said strategies further comprising the steps of;
using, in response to a situation wherein said header area is useable by said recording system, said indicia of location in said header are to locate said selected data block by counting said servo control pulses on said second longitudinal track;
using, in response to the situation wherein said header area is unusable by said recording system, data stored on said servo control track to first locate said sector mark delineating the sector preceding the sector containing said selected data block by counting said servo control pulses on said second longitudinal track prior to location closed selected data block; and
using, in response to a situation wherein said header area is useable by said recording system, and wherein said indicia of location of said data blocks is not consistent with said indicia of location in said command from said host computer, data stored on said second longitudinal track to first locate one of said position marks delineating the file containing said selected data block prior to locating said selected data block.
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Abstract
A novel method is disclosed for performing a high speed search for a selected data block or data file utilizing any one of several presently existing helical scan tape formats which utilize, in addition to the helically scanned tracks, one or more longitudinal tracks for recording indexing information indicative of the location of data blocks and file marks stored on the associated helical tracks. Data file location information is written to a header area on a series of helical tracks and to one (or more) of the longitudinal tracks when a data block or a file mark is written to a tape. A high speed search for a desired data block or data file can then be performed using this track location information.
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Citations
4 Claims
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1. In a data recording system using magnetic tape for storing data, said recording system connected to a host computer, said recording system using a recording format on said magnetic tape employing a plurality of helically scanned tracks for storing said data, including a first longitudinal track for storing magnetic tape position information indicative of location of said data and a second longitudinal track containing position marks and servo control pulses, said position information being written at equally spaced predetermined locations on a said first longitudinal track, said position information comprising a plurality of file marks and sector marks said data being logically segmented into files containing sectors comprising data blocks, and wherein said data recording system uses a tape drive control unit to store a memory copy of said header area from said magnetic tape, a method for locating a selected block in response to a command from said host computer, said command including indicia of location of said selected data block comprising the steps of:
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placing a header area on said helically scanned tracks for locating said selected block, said header area containing indicia of location of said data blocks comprising the number of said servo control pulses between said header area and a location of each of said blocks; reading said memory copy of said header area to determine whether valid magnetic tape position information is contained therein; and employing redundant strategies for locating said selected data block, one of said strategies being selected according to a data integrity of said header area, said strategies further comprising the steps of; using, in response to a situation wherein said header area is useable by said recording system, said indicia of location in said header are to locate said selected data block by counting said servo control pulses on said second longitudinal track; using, in response to the situation wherein said header area is unusable by said recording system, data stored on said servo control track to first locate said sector mark delineating the sector preceding the sector containing said selected data block by counting said servo control pulses on said second longitudinal track prior to location closed selected data block; and using, in response to a situation wherein said header area is useable by said recording system, and wherein said indicia of location of said data blocks is not consistent with said indicia of location in said command from said host computer, data stored on said second longitudinal track to first locate one of said position marks delineating the file containing said selected data block prior to locating said selected data block. - View Dependent Claims (2, 3, 4)
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Specification