Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data in specific format
Reexamination Certificate
2001-07-31
2004-12-21
Sniezek, Andrew (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data in specific format
C360S053000, C360S031000
Reexamination Certificate
active
06833970
ABSTRACT:
FIELD OF THE INVENTION
This invention provides an improved data reader suitable for a data storage device, which may be a tape drive arranged to receive data from a computer, or the like. The invention also provides related methods and devices incorporating such a reader,
BACKGROUND AND OBJECTIVES
An example of a data storage device is the tape drive, which receive user data from computers, particularly, but not exclusively to back-up the user data held on the computer onto a data-holding medium. In such back-up applications it is of prime importance that the user data is retrievable, since generally, this copy is the back-up copy that will only be required if the original copy has been lost or damaged. Therefore, there is an ongoing need to ensure that backup data storage devices are as robust and secure as possible.
Once user data has been stored on the data-holding medium it can be held there for long periods. To recover the user data from the data-holding medium the data storage device must read the data-holding medium and regenerate the user data originally stored there. In some devices the user data backed-up on the dataholding medium accounts for only roughly 80% of the overall information held on the data-holding medium. The remaining roughly 20% of the information is header, error correction information that attempts to make the user data as secure as possible.
Therefore, in order to read the user data the storage device must accurately detect the user data within all of the information held on the data-holding medium. In view of the amount of information other than user data that is held on the data-holding medium, this can be problematic,
It is known to provide markers, sometimes referred to as data separator fields (DSS fields), that identify when significant occurrences are about to happen within the information that is held on the data-holding medium. For example, it is known to provide a marker before a set of user data occurs on the data-holding medium. It is also known to provide non-user data, including header information that specifies the contents of portions of the user data.
It is an object of the present invention to provide a data reader suitable for a data storage device that addresses the problems discussed above.
SUMMARY
According to a first aspect of the invention there is provided a data reader arranged to read a data-holding medium containing data comprising both user and non-user data, set data being held in at least one set, and each said set being arranged into datasets, said non-user data holding information relating to said user data and being interspersed therewith, said data reader comprising at least one read head arranged to read said data-holding medium and generate a data signal comprising user data and non-user data, said non-user data being arranged to identify said user data within said sets, processing circuitry being arranged to receive and process said data signal and obtain said user data from said data signal using said non-user data to identify said user data within said data signal.
An advantage of such an apparatus is that it does not rely on a marker stored on the data-holding medium to identify the start of user data. Prior art data storage devices have relied on detecting this marker to identify that user data is about to occur. A problem with detecting the marker in this manner is that if the marker is not detected, or data is interpreted as the marker, then data can be lost.
Relying on the information held in the non-user data is advantageous because it can provide a more robust approach and therefore, is it less likely that data will be lost.
The sets of data may themselves be arranged into larger groupings, or datasets. The sets may be arranged on the data-holding medium such that the datasets may overlap one another. The processing circuitry may be arranged to occupy a state reflecting, whether or not the sets of data being read by the reader must be from the same dataset, or whether the sets are possibly from a plurality of datasets. I.e. the data is in an overlap zone in which datasets can overlap one another. An advantage of causing the processing circuitry to occupy such state is that it provides a convenient way of noting the nature of the data being read from the data-holding medium. The processing circuitry may be arranged to occupy a state in any one or more of the following manners: having a flag set, having a state machine in which the occupied state varies, setting a register, altering a memory location, etc.
In the preferred embodiment only two datasets can overlap one another, and therefore, two state machines are provided: one state machine provided in relation to each of the datasets.
Further, when data is written to the data-holding medium it may overwrite data already in existence on the data-holding medium. Data that overwrites existing data in this manner is generally written at the end of a dataset that exists on the data-holding medium. However, there may be a latency between a dataset finishing on the data-holding medium and the stat of the over written data, which can result in a portion of data from a dataset that should have been over written remaining. Therefore, at the end of each dataset on the data-holding medium there may be an overwrite zone in which a first dataset can finish and data from a second dataset can start before the first dataset has finished (due to the second dataset having overwritten the first). The processing circuitry may be arranged to occupy a state reflecting whether or not data being read from a data-holding medium is in an overwrite zone.
Further, the processing circuitry may be arranged to occupy a state arranged to reflect when data being read from a data-holding medium is beyond an overwrite zone.
A zone detector may be provided to interpret the non-user data and determine whether the user data must be from the same dataset, or could possibly be from a plurality of datasets. Preferable, the zone detector is arranged so that it controls the state of the processing circuitry.
The reader may comprise a plurality of read-heads, each of which is arranged to read a separate channel of data, preferably in parallel with one another. In the preferred embodiment the reader comprises 8 read heads, although the reader could comprise any number of read heads. For example the reader may comprise 2, 3, 4, 5, 6, 7, 9, 10, 11, 12, 13, 14, or more read heads. An advantage of providing more than one read head in this manner is that the rate at which data can be read from the data-holding medium is increased.
Conveniently, the reader comprises a controller that is arranged to determine whether user data read from the data-holding medium should be accepted and stored in a memory of the reader. Preferably, the controller includes the at least one state machine.
According to a second aspect of the invention there is provided a data storage device incorporating a data reader according to the first aspect of the invention.
In the preferred embodiment the data storage device is a tape drive. Such a tape drive may be arranged to read data held in any of the following formats LTO (Linear Tape Open), DAT, (Digital Audio Tape), DLT (Digital Linear Tape), DDS (Digital Data Storage), or any other format. Although in the preferred embodiment the tape is LTO format.
Alternatively, the data storage device may be my one of he following: CDROM drive, DVD ROM/RAM drive, magneto optical storage device, hard drive, floppy drive, or any other form of storage device suitable for storing digital data.
According to a third aspect of the invention there is provided a method of reading data from a data-holding medium containing user data held in a plurality of sets and interspersed with non-user data, said non-user data-holding information relating to said user data, the method comprising reading said non-user data to identify said user data within said sets and obtain said user data from said data-holding medium said method further comprising arranging said sets of user data into datasets, the identity of
Davidson Dan I
Hewlett--Packard Company
Sniezek Andrew
LandOfFree
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