Write pass identifier

Details Write pass identifier Write pass identifier

1999-02-12

2001-08-28

Faber, Alan T (Department: 2651)

Dynamic magnetic information storage or retrieval

General processing of a digital signal

Data in specific format

C360S053000, C360S031000

Reexamination Certificate

active

06282040

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to data storage devices and particularly although not exclusively to a method of writing data to include data dropout protection in a linear tape data storage device.
BACKGROUND TO THE INVENTION
In order to store digital electronic data it is known to use magnetic tape data cartridges, 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.
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 onto the magnetic tape incorporates redundant data from which the original data can be recovered if there is corruption of the data recorded on tape. Such corruption may occur for a variety of reasons, for example, 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. In such cases, on reading the data, areas of corruption are detectable because the data is absent or a usable data signal is indistinguishable in a read signal produced by a read head.
However, another situation where corruption of data can arise and which requires the use of encryption for its correction is where a tape is overwritten and old pre-recorded data from a previous write operation has not been completely erased. This can occur if the tape momentarily loses contact with the read/write head and the new data has not been written over the old. This condition is known as a “data drop out”. It is possible that, when the data is subsequently read from tape, old incorrect data could be returned to the host. Since the old data read is present, and may be uncorrupted, it may be mistaken for the correct data which was intended to overwrite the old pre-recorded data.
As the density of data stored on tapes increases and the physical size of tape tracks decreases then the need to correct data dropout defects becomes more important, because increasingly larger amounts of pre-recorded data may fail to be over-written.
A further problem in linear tape data storage devices is identifying where a set of recorded data ends on the tape. Where a new set of data has been overwritten over old pre-recorded data, over a length of tape, the old pre-recorded data, which was written in a same general format as a set of new data overwriting the pre-recorded data, needs to be distinguished from the new data, in order to avoid reading the old data, and mistaking it for new data.
SUMMARY OF THE INVENTION
Specific embodiments and methods according to the present invention aim to improve the detection of data dropouts when reading data from high data density tape systems, and thereby improve reliability of such devices.
Specific methods according to the present invention, recognize that if a most recently written data on a tape can be uniquely identified, then old pre-recorded data, which may be incompletely overwritten by the new data, may be recognized and discarded by a data reading device.
According to a first aspect of the present invention, there is provided a method of writing data to a data storage medium, said method comprising the steps of:
performing a write operation to write data to said data storage medium; and
for each said write operation, writing an identifier data to said data storage medium, said identifier data uniquely identifying said write operation.
Data is written in sets of data blocks, and an end of a said set of data blocks is marked by recording an end of data indicator. When data is written to the data storage medium such that this causes existing pre-recorded data on the data storage medium to be overwritten, then unless the write operation starts at an existing end of data indicator field recorded on said data storage medium, a value of the identifier data is incremented. Preferably the value of the identifier is incremented above a value of an existing identifier data associated with the existing pre-recorded data on the data storage medium.
Preferably, said data storage medium comprises an elongate tape, and a said write operation comprises a write pass along a length of said tape.
Said method may comprise performing a plurality of said write operations in a sequence, wherein for each said write operation a corresponding respective unique said identifier data is assigned, identifying said write operation.
The data written by a first said write operation having a first said identifier data may be overwritten by a second said write operation having a second said identifier data, wherein said second identifier data is incremented in value with respect to said first identifier data.
Preferably, said written data is partitioned into a set of data blocks, and a said identification data is included in each said data block.
The invention includes a tape data storage device capable of writing data to a tape data storage medium, wherein:
said device is operable to perform a write operation to write data to said tape data storage medium; and
for each said write operation, said device is operable to write an identifier data to said data storage medium, said identifier data identifying said write operation.
Where the device writes data to a data storage medium which has existing pre-recorded data, and the writing of the data causes the existing pre-recorded data to be overwritten, unless the write operation starts at an existing indicator indicating an end of the pre-recorded data on the data storage medium, then the value of the identifier data of the written data is incremented compared to a previous value of said identifier data.
According to a second aspect of the present invention there is provided a method of formatting data recorded on a data storage medium so as to include information relating to a vintage of said data, said method comprising steps of:
arranging a byte stream of data into a plurality of data blocks; and
adding a data block header to each said data block,
wherein said data block header uniquely identifies a vintage of said recorded data.
suitably, on an occasion that data is written to the data storage medium which causes existing pre-recorded data on the data storage medium to be overwritten, an identifier data field within the data block header is incremented. The increment is made relative to a previous value of said identifier data.
Preferably, said step of adding a data block header to each said data block comprises:
creating an identifier field within said data block header; and
incrementing or changing said identifier field when data is written to said data storage medium.
Said write pass indicator may be incremented whenever a write operation causes pre-recorded data to be overwritten.
Said identifier field preferably contains data identifying a write pass operation.
Preferably, said data storage medium comprises a magnetic tape.
The invention includes a method of encoding data written to tape so as to distinguish over-write data from pre-recorded data, said method comprising the steps of:
reading a first write pass identifier of said pre-recorded data already recorded on tape;
arranging a byte stream of said overwrite data into a plurality of data blocks;
to each data block, adding a block header containing a second write pass identifier identifying a write operation in which said data is over-written on said pre-recorded data,
wherein said second write pass identifier of said overwrite data is incremented compared to said first write pass identifier of said pre-recorded data.
The invention includes an encoding device capable of encoding data written to tape so as to distinguish overwrite data from pre-recorded data, wherein said encoding device comprises:
means operable to read a first write pass identifier of said pre-recorded data already recorded on tape;
means operable to arrange a byte stream of said overwrite data into a plurali

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