Closed loop write verification in a disc drive

Details Closed loop write verification in a disc drive Closed loop write verification in a disc drive

1999-06-04

2001-07-24

Neal, Regina Y. (Department: 2651)

Dynamic magnetic information storage or retrieval

General processing of a digital signal

Data verification

C360S031000, C360S046000

Reexamination Certificate

active

06266202

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to the field of disc drive devices and more particularly, but without limitation, to performing real-time, closed loop write verification through magnetic coupling of read and write elements of a disc drive head.
BACKGROUND OF THE INVENTION
Disc drives are used as primary data storage devices in modern computers and computer networks. A typical disc drive includes a head-disc assembly (HDA) housing one or more magnetic discs which are rotated by a spindle motor at a constant high speed and accessed by an array of read/write heads which store data on tracks defined on the disc surfaces. Electronics used to control the operation of the HDA are provided on a printed wiring assembly (“circuit board”) which is mounted to the underside of the HDA.
Each head is typically provided with separate read and write elements, with a common configuration utilizing a thin film, inductive write element and a magneto-resistive (MR) read element. Data are written by passing a write current through the write element, with the write current generating a time-varying magnetic field which selectively magnetizes the disc surface. Previously written data are read using the read element to transduce the selective magnetization of the disc to generate a readback signal which is used by a read channel to reconstruct the data. An interface circuit buffers and controls the transfer of data between the disc and a host computer.
Technological advancements in the art have resulted in continued improvements in disc drive data storage capacities and transfer rates. It has not been at all uncommon for each successive generation of drives to provide substantially twice the data storage capacity as the previous generation, at an equal or improved data transfer rate. Design cycle times are also being shrunk to the point that a new generation of drives is typically introduced into the marketplace every few months.
The commercial success of disc drives is not only a result of the costeffective manner in which vast amounts of user data can be stored and retrieved, but also in the demonstrated reliability of the typical disc drive over a relatively long operational life. Nevertheless, for applications where data integrity is critical, methodologies have been developed to further enhance the ability of disc drives to consistently and accurately store and retrieve data.
One such methodology is the grouping of a plurality of drives into a multi-drive array, sometimes referred to as a RAID (“Redundant Array of Inexpensive Discs”). Since their introduction, RAIDs have found widespread use in a variety of applications requiring significant levels of data transfer, capacity and integrity performance. Various RAID architectures employ mirroring (simultaneously writing data to two or more identical drives), striping (writing portions of the data across multiple drives) and interleaving (employing various types of error detection and correction schemes at multiple levels to ensure data integrity).
Another particularly useful methodology to maximize data integrity is through the use of write verification, which involves the writing of data to a disc followed by a subsequent read operation where the previously stored data are retrieved from the disc to ensure the data were correctly written. However, such write verification operations undesirably decrease the data transfer performance of the disc drive, as each write operation requires each sector to which data are written to be accessed at least twice: first, when the data are written, and second, when the data are subsequently read back for verification. Conventional write verification techniques accordingly impose a severe penalty on disc drive performance, limiting data transfer rates to levels substantially below that which would be otherwise achievable.
As consumer demands continue to drive further advances in data transfer rate and integrity performance, there remains a continual need for improvements in the disc drive art whereby these often mutually exclusive characteristics can be optimized. It is to such improvements that the present invention is directed.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and method for performing closed-loop, real time write verification in a disc drive.
In accordance with a preferred embodiment, the disc drive has a rotatable magnetic disc, and a head with read and write elements with the read element being magnetically coupled to the write element.
Data are written to the disc by first generating a write current signal indicative of the data to be written and then applying the write current signal to the write element. In response, the write element generates a time-varying magnetic field which magnetizes the disc to write the data to the disc, while simultaneously inducing a readback signal in the read element as a result of the magnetic coupling of the read element to the write element. The readback signal is used to verify the accuracy of the writing operation.
More particularly, a set of output data is reconstructed from the readback signal and compared to the data originally written to the disc. In this manner, the data written to the disc can be verified on-the-fly, eliminating the need for a subsequent read operation to verify the data.
The write verification can be performed during substantially all write operations, or on a sampled basis as a diagnostic tool or error recovery routine. One read channel configuration includes the use of a single partial response, maximum likelihood (PRML) data path that switches between two different sets of channel parameters, with one set used during normal readback operations and the other set used during on-the-fly write verification. An alternative read channel configuration employs a PRML data path for normal readback operations in parallel with a peak-detect data path used for write verification detection.
These and various features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.


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