Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data in specific format
Reexamination Certificate
1998-10-30
2001-08-28
Faber, Alan T. (Department: 2753)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data in specific format
C360S047000, C360S053000, C714S006130, C714S701000
Reexamination Certificate
active
06282039
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of redundancy coding for scratch protection in a linear tape data storage device and medium.
BACKGROUND TO THE INVENTION
In order to store digital electronic data it is known to use magnetic tape cartridges comprising a pair of reels, which are inserted into a tape drive unit having a plurality of read/write heads. Typically, such magnetic tape storage devices may be used to back up data generated by a host device, eg a computer, or to store data generated by test or measurement instruments. For example, the conventional SureDrive® data storage unit manufactured by Hewlett Packard Company is capable of storing 8 GBytes of data on a single cassette cartridge. In the conventional SureDrive series 12000 unit, by including a plurality of cassette cartridges, a data storage capacity 48 Gbytes is achieved in a single compact drive assembly of dimensions of the order of a few tens of centimeters.
Conventional tape drive units operate to draw an elongate magnetic tape past a read/write head. Tape speeds past the heads are relatively slow, of the order of a few centimeters per second.
In the conventional tape drive, electronic circuitry is provided to encrypt the digital data to be stored, using an algorithm which applies redundancy encryption to the original digital data, so that the data recorded on to the magnetic tape incorporates redundant data from which the original data can be recovered if there is corruption of the data recorded on the tape. Such corruption may occur at the edges of the tape due to non-uniform coating of the tape with magnetic material, or due to variations in alignment of the tape with the read/write head.
An on-going objective of magnetic tape drive development is to increase the amount of data which can be stored on a magnetic tape, and to reduce the size of tapes and tape drives thereby allowing drives to be used in an increasing range of applications. Achieving such objectives involves increasing the density of recorded data per unit area of tape.
However, as data density is increased and tape sizes become smaller, loss of data due to tape damage caused by tape stretching, or scratching of the tape becomes more problematic as any such damage may obliterate larger amounts of data.
It is another ongoing objective of tape drive development to increase the reliability of tapes and tape drives whilst reducing their cost.
SUMMARY OF THE INVENTION
Specific embodiments and methods according to the present invention aim to maintain integrity of data under conditions of scratched or damaged tape surface in high data storage density tape systems, and thereby improve reliability of such devices.
According to one aspect of the present invention there is provided a method of redundancy coding data comprising the steps:
forming a plurality of data frames by arranging a byte stream of data into a plurality of data sets, and for each data set, applying a redundancy coding to said data set to obtain a corresponding data frame; and
for each said data frame, distributing said redundancy coding of said data frame over all other said data frames of the plurality of data frames.
Preferably, said step of applying a redundancy coding comprises:
arranging a said data set into a 2 dimensional array;
applying a first coding algorithm to said data set in a first dimension to obtain a plurality of first codewords; and
applying a second coding algorithm to said data set in a second dimension to obtain a plurality of second codewords.
Preferably, said step of distributing redundancy coding comprises for each said data frame, distributing bytes of each second codeword of said data frame over said plurality of data frames.
Preferably, said step of distributing said redundancy coding comprises partitioning each said data frame into a plurality of track blocks, each track block comprising a plurality of said first codewords read sequentially as rows of said data frames, and for each second codeword of a said data frame, distributing bytes of said second codeword across a plurality of said track blocks of said plurality of data frames.
According to a second aspect of the present invention, there is provided a method of storing data on a magnetic tape data storage medium, said method comprising the steps of:
partitioning said data into a plurality of data sets;
applying a redundancy coding to each said data set to produce a plurality of corresponding data frames; and
recording each said data frame of the plurality of data frames onto a length of tape,
wherein a redundancy coding of each said data frame is distributed over said plurality of recorded data frames.
Preferably, for each said data set, a said redundancy coding comprises a plurality of first codewords, and a plurality of second codewords, and said distribution of redundancy coding may comprise bytes of said second codewords arranged diagonally across a length of said tape.
A plurality of physical data tracks on a length of magnetic tape data storage medium are substantially parallel to each other, and extend along a main length of said magnetic tape. Said data frame suitably comprises a plurality of first codewords in a first dimension and a plurality of second codewords in a second dimension. Said first codewords are suitably distributed along a length of the tape in a direction parallel to a direction of travel of the tape, whereas the second codewords may be distributed on the tape in a direction transverse to a direction of travel of the tape.
By redundancy coding a data frame in two dimensions, and distributing a data frame across different physical tracks of the tape, redundancy data corresponding to user data recorded on a first physical track is distributed across a plurality of other physical tracks. Loss of data from a first physical track due to tape damage, for example elongate scratches along the track may be recoverable from redundancy coded data contained in adjacent, undamaged tracks.
The two dimensional data frame comprises a plurality of data rows and data columns. Recording the data frame may comprise recording a said row within a single corresponding said data track and recording a said column across a plurality of said data tracks. Recording may comprise recording all bytes of a said row in a single track along a main length of said tape and recording bytes of a said column distributed in a direction across a width of said tape and in a direction along a main length of said tape.
Suitably, physical tracks over which a two-dimensional data frame are distributed, are sufficiently far apart that adjacent tracks containing data of a same data frame will not be obliterated by a same elongate scratch.
Preferably said data frame comprises a plurality of first codewords in a first dimension, and said method may comprise the step of partitioning said two dimensional array into a plurality of track blocks, each track block comprising a plurality of said rows and said step of recording may comprise recording each said track block to a corresponding said physical track.
The arrangement is suitably such that each said second codeword has at most one byte in common with each track block. A first codeword may operate to locate a position of an error in said two dimensional data frame, and the second codeword may operate to correct an error itself.
Suitably, a plurality of bytes of a second codeword are distributed substantially uniformly over an area of tape occupied by a plurality of recorded data frames. By distributing bytes of a second codeword substantially diagonally across a length of the tape and by spreading out the bytes substantially uniformly over a length occupied by an area of the tape corresponding to the plurality of the recorded data frames, improved protection against longitudinal scratches in a direction parallel to a length of the tape, and transverse scratches in a direction normal to a length of the tape may be obtained.
According to a third aspect of the present invention, there is provided a method of storing data on a magnetic tape data
Faber Alan T.
Hewlett--Packard Company
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