Error detection/correction and fault detection/recovery – Pulse or data error handling – Memory testing
Reexamination Certificate
1999-03-12
2001-10-16
Chung, Phung M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Memory testing
Reexamination Certificate
active
06304986
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to a magnetic disk system for reading/writing data from/in a magnetic disk serving as a recording medium. More particularly, the present invention relates to a magnetic disk apparatus having an inspection function of detecting a defect in a magnetic disk and a method of inspecting a recording medium in the magnetic disk apparatus.
BACKGROUND OF THE INVENTION
In magnetic recording technology, desired data is generally recorded by magnetizing the surface of a fixed disk. The disk used in the magnetic disk apparatus inevitably has a rough disk surface and nonuniform magnetic material to some extent. It is desired to improve the density at which information can be recorded and read. The total memory storage capacity or recording density is proportional to the number of tracks and the linear density on the surface of a disk. The number of tracks is dependent upon the width of the tracks.
In order to achieve more narrow tracks, the need to more precisely control the surface conditions of the disks has become increasingly important. A defect or bump on the surface of the disk can degrade or grow, thereby resulting in an unuseable area on the disk. There is a problem of growing defects over the life of a media. A growing defect is a defect on the media that enlarges over time due to physical degradation of the media. The media can become damaged due to dust, scratches, etc. Areas that are not used often may have growing defects due to head movement across the surface during a seek. Moreover, any unwanted contact between the head and magnetic surface can also lead to wear and the accumulation of debris on the disk causing random signal modulations. Typically, during non-use of the drive (e.g., after the drive is idle for 1 second), the heads just sweep or move over media without any reading or writing. This prevents the heads from staying in one location which would otherwise lead to media wear at that location.
Flaws or defects in the disk surface manifest themselves as missing bits or extra bits of data (i.e., single bit errors). Missing bits are reductions in the amplitude of the envelope of the signal, usually over a small number of bits (e.g., 1-4 bits), such that the amplitude falls below a channel-detector clipping level. The number of missing bits observed depends on the setting of the clipping level in the readback channel.
Several methods exist for detecting defects on the surface of a disk. One method involves performing media verification on the disk surface prior to packaging the disk and shipping it to the consumer or end user. However, this technique only locates the defects that exist originally, and will not locate defects that form after shipment of the disk and during usage. Another technique that can be used is for the end user to reformat the entire disk. This will locate any existing defects. However, this technique erases the existing data, so that the data must be saved elsewhere during the reformatting. This is very inconvenient for the user. Furthermore, typically, when data is read from or written to a disk, the media is checked at the critical locations with error correction coding (ECC). In this manner, heavily used areas are checked often for defects. However, areas that are not used frequently are not checked often for defects. Thus, at these locations, growing defects can form and grow without early detection.
Although the art of error detection on media is well developed, there remain some problems inherent in this technology, particularly early detection of growing defects. Therefore, a need exists for a system and method of detecting growing defects that overcomes the drawbacks of the prior art.
SUMMARY OF THE INVENTION
The present invention is directed to a system and method of detecting defects on a surface of a recording medium in a magnetic disk apparatus, comprising: detecting an idling state of the magnetic disk apparatus; determining a duration that the recording medium has been in use; sequentially detecting the presence/absence of defects on the surface of the recording medium, responsive to the duration and the idling state, beginning at a start location of the recording medium; reallocating data located at a detected defect to a predetermined storage area; and mapping the detected defect in a defect location map.
According to one aspect of the present invention, the idling state is detected when the magnetic disk apparatus has been idle for a predetermined time. Preferably, the predetermined time is approximately 1 second.
According to another aspect of the present invention, the predetermined storage area is a predetermined location on the recording medium. Preferably, the start location is a random track/sector on the recording medium.
According to another aspect of the present invention, the duration is a spin count of a number of spin ups or a number of spin downs. Determining the duration comprises retrieving the spin count from a storage means. Preferably, the storage means is a Z-track of the recording medium.
According to another aspect of the present invention, the spin count is reset after the entire surface of the recording medium has been sequentially detected for the presence/absence of defects.
According to another aspect of the present invention, the spin count is incremented either each time the magnetic disk apparatus spins up or spins down.
According to another aspect of the present invention, the duration is compared to a predetermined threshold. The defect detection is begun when the idling state has been detected and when the duration exceeds the predetermined threshold. Preferably, the duration is a number of spin ups or a number of spin downs and the predetermined threshold is about 200. Moreover, the predetermined threshold is programmable.
According to another aspect of the present invention, the sequential detection of the presence/absence of defects comprises error correction coding.
According to further aspects of the invention, the sequential defect detection is interrupted responsive to a command received from a host system. The command is executed and the sequential detection resumes beginning at a random location on the recording medium.
REFERENCES:
patent: 5247254 (1993-09-01), Huber et al.
patent: 5751947 (1998-05-01), Arakawa
patent: 5792947 (1998-08-01), Pogrebinsky et al.
Ma Yiping
Pan Weimin
Peters Eric R.
Washburn Klinton D.
Chung Phung M.
Iomega Corporation
Woodcock Washburn Kurtz Mackiewicz & Norris LLP
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