Disk Drive Data Recovery via Defective Bit Detection
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Solution Overview
Problem
Magnetic recording disk drives with bit-patterned-media face challenges in identifying and correcting hard bit errors caused by defective data islands, which are time and memory-intensive to track, especially when defects occur during operation.
Innovation Solution
A method to determine the location of defective bits in a failed sector by writing and reading predetermined nondata patterns, updating the read channel state, and using error correction codes to decode and relocate data, allowing for efficient identification and correction of hard bit errors without extensive defect tracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the entire disk is mapped during manufacturing or idle time to catalogue defective islands, then the locations of defective bits can be identified, but the process is time-consuming and memory-space consuming
Solution Approach 1:
The patent performs preliminary defect detection by writing test patterns to sectors and identifying defective bits before normal operation. The read channel state is updated with defect information in advance, so that when a sector failure occurs, the ECC can immediately use the pre-identified defective bit locations for decoding, avoiding time-consuming real-time defect mapping.
Solution Approach 2:
The patent extracts only the necessary defect information (defective bit locations) from the read channel state and stores it in a compact format within the ECC structure. Instead of maintaining a complete disk map, only the relevant defective bit positions are retained and used for error correction, significantly reducing memory space requirements.
2Measurement precision
If the entire disk is mapped during manufacturing or idle time to catalogue defective islands, then the locations of defective bits can be identified, but the process is memory-space consuming
Solution Approach 1:
The patent extracts only the necessary defect information (defective bit locations) from the read channel state and stores it in a compact format within the ECC structure. Instead of maintaining a complete disk map, only the relevant defective bit positions are retained and used for error correction, significantly reducing memory space requirements.
Solution Approach 2:
The patent applies defect tracking locally at the sector level rather than globally across the entire disk. Each sector maintains its own defect information in the read channel state, allowing defective bit locations to be identified without allocating memory for a comprehensive disk-wide defect map.
3Measurement precision
If conventional defect tracking methods are used, then defective bits can be identified, but the method is ineffective if defects get created during operation
Solution Approach 1:
The patent implements a feedback mechanism where the read channel state is continuously updated with defect information from read operations. When a sector is read, the read channel analyzes the signal and updates the defective bit locations in the read channel state, ensuring that newly created defects are automatically detected and incorporated into the error correction process for subsequent operations.
Solution Approach 2:
The patent makes the defect tracking system dynamic by continuously updating the read channel state during normal read operations. Instead of a static defect map created during manufacturing, the system adapts to new defects that arise during operation, automatically incorporating them into the error correction capability.
4Reliability
If error correction codes are used without pointers to unreliable bits, then the ECC can decode data, but the allowed number of bit errors is limited
Solution Approach 1:
The patent performs preliminary identification of defective bit locations using the read channel state before the ECC decoding process. The locations of unreliable bits are determined in advance and used to guide the ECC decoding, allowing the error correction code to focus its correction capability on the identified defective positions, thereby increasing the total number of correctable errors.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate decoding of data from failed sectors by identifying and marking unreliable bits, reducing the need for extensive defect tracking and enabling real-time correction of hard bit errors, thus improving data recovery efficiency in disk drives.
Implementation Method 1
Magnetic recording disk drives with bit-patterned-media (BPM) have been proposed to increase the data density. In BPM, the magnetic material on the disk is patterned into small isolated data islands arranged in concentric data tracks.
Implementation Method 2
When the data is read back from a sector the ECC detects errors and uses the error correction bits to correct the errors.
Data Source
AI summary
A magnetic recording disk drive determines the locations of defective bits in a failed data sector, and allows for the error correction code (ECC) to correctly decode the data from the sector. After a sector has failed decoding, the digitized waveform and the read channel state from the failed sector are stored in memory. A nondata pattern is written to the failed sector and read back to determine the locations of the defective data bits in the failed sector, which are then used to update the read channel state. The data pattern from the failed sector, with the identified bit error locations, is attempted to be decoded. If the decoding is successful then the sector is marked as bad and the correctly decoded data pattern is written to a different region of the disk, for example physical sectors specifically intended for use as spare sectors.