Track Measurement for Data Storage Devices Using Off-Track Read Capability
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Solution Overview
Problem
Conventional track measurement tests in Shingled Magnetic Recording (SMR) applications become unreliable due to increased track proximity, leading to inaccurate and non-repeatable results, as they fail to account for Track Mis-Registration (TMR) and Adjacent Track Interference (ATI), which affect the placement and integrity of data on magnetic disks.
Innovation Solution
The proposed solution involves improved track measurement processes that account for variations in track placement caused by TMR, using a combination of Data Storage Device (DSD) and host device to perform tests, calculating average Off-Track Read Capability (OTRC) values and their standard deviations to determine accurate track positioning, and adjusting the system squeeze settings to minimize the impact of TMR and ATI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If track proximity is increased to improve storage density in SMR applications, then storage capacity increases, but measurement reliability deteriorates due to TMR and ATI effects
Solution Approach 1:
The patent segments the track measurement process into multiple individual sector readings rather than treating the track as a single unit. By reading and evaluating multiple sectors (e.g., 10-20 sectors) and calculating statistical metrics like average OTRC and standard deviation, the method isolates the effects of TMR and ATI from random measurement variations, thereby maintaining measurement reliability despite increased track proximity in SMR applications
Solution Approach 2:
The patent implements a feedback mechanism where the standard deviation of OTRC values across multiple sectors is calculated and used to determine whether to accept or reject the measurement. If the standard deviation exceeds a threshold, indicating high variability likely due to TMR or ATI, the measurement is rejected and retried. This feedback loop ensures that only reliable measurements are accepted, maintaining measurement reliability even when tracks are closely spaced
2Device complexity
If conventional track measurement tests are used in SMR applications, then test simplicity is maintained, but measurement accuracy deteriorates due to unaccounted TMR and ATI effects
Solution Approach 1:
The patent performs preliminary actions by reading multiple sectors before making a final measurement determination. Instead of taking a single reading, the system pre-reads multiple sectors (e.g., 10-20 sectors) and calculates statistical metrics including average OTRC and standard deviation. This preliminary statistical analysis filters out measurements affected by TMR and ATI, improving measurement accuracy while adding manageable complexity to the testing process
Solution Approach 2:
The patent changes the measurement parameters from a single OTRC value to a statistical distribution of OTRC values across multiple sectors. By calculating the average OTRC and its standard deviation, the method transforms the measurement approach to account for variations caused by TMR and ATI. The standard deviation serves as a quality metric to determine measurement validity, thereby improving measurement accuracy in SMR applications
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
This approach enhances the accuracy and repeatability of track measurement tests by considering multiple sectors and statistical variations, reducing the influence of TMR and ATI, thereby improving the reliability of track placement and data integrity in SMR applications.
Implementation Method 1
A magnetic head of the DSD can magnetically read and write data in tracks on a surface of the disk
Data Source
AI summary
Track placement on a disk of a Data Storage Device (DSD) including writing test data in a plurality of sectors in a test track on the disk. An adjacent track on the disk is written offset from the test track by an offset distance. Data is read from the test track from an Off-Track Read Capability (OTRC) position outside of the test track. An OTRC value is determined for each sector of the plurality of sectors by varying the OTRC position and determining whether the sector meets a criterion for correctly reading data from the sector. An average OTRC value and a standard deviation are calculated for the plurality of sectors. If it is determined that the average OTRC value is greater than or equal to the predetermined multiple of the standard deviation of the OTRC values, the adjacent track is rewritten at a decreased offset distance.