Shingled Magnetic Recording Disk Drive ECC Zone Adaptation
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Solution Overview
Problem
Shingled magnetic recording (SMR) hard disk drives face challenges in optimizing error correction code (ECC) strength due to fixed settings, which can result in wasted disk space or uncorrectable data errors, as they do not adapt to changing environmental conditions or data types.
Innovation Solution
The SMR HDD dynamically adjusts ECC strength by dividing the disk recording surface into zones based on time averages of the position-error signal (PES) and optionally monitoring data stream types, allowing for varying numbers of ECC sectors per zone to optimize error correction according to current conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed value for the number of ECC sectors is used, then the drive can be manufactured with a determined error correction capability, but the ECC strength cannot adapt to changing environmental conditions or data types, resulting in either wasted disk space or uncorrectable data errors
Solution Approach 1:
The patent divides the disk recording surface into multiple zones, each with a different number of ECC sectors. The system dynamically selects which zone to write data to based on real-time monitoring of position-error signal (PES) time averages and data stream characteristics. This allows the ECC strength to adapt dynamically to changing environmental conditions (through PES monitoring) and data types (through seek pattern analysis), resolving the contradiction between fixed manufacturing settings and the need for adaptive error correction capability.
2Reliability
If the number of ECC sectors is increased to handle worst-case environmental conditions, then data integrity is improved under high TMR conditions, but disk space is wasted under normal operating conditions
Solution Approach 1:
The patent segments the disk recording surface into multiple zones, where each zone has a different number of ECC sectors associated with it. Zone 1 might have 2 ECC sectors per data block, while Zone 2 might have 4 ECC sectors per data block. This segmentation allows the system to provide stronger error correction only where and when needed (under high TMR conditions), rather than uniformly across the entire disk, thus improving data integrity under adverse conditions while maximizing usable disk space under normal conditions.
Solution Approach 2:
Different regions (zones) of the disk are assigned different ECC strengths based on local conditions. The system monitors PES time averages locally for each zone and selects the appropriate zone for writing data. This means that error correction strength is locally optimized rather than globally uniform, allowing high reliability in zones experiencing high TMR while maintaining high storage efficiency in zones with good operating conditions.
3Quantity of substance
If the number of ECC sectors is decreased to maximize disk space, then areal density is improved, but the drive cannot correct errors under challenging environmental conditions or with certain data types
Solution Approach 1:
The system dynamically adjusts the number of ECC sectors used for each data block based on real-time monitoring of PES time averages and data stream characteristics. When challenging conditions are detected (high PES averages indicating high TMR, or frequent seeks indicating short data streams), the system automatically selects zones with more ECC sectors. This dynamic adjustment allows the drive to maximize disk space utilization under normal conditions while ensuring adequate error correction capability when needed.
4Reliability
If ECC strength is increased for short data streams with frequent seeks, then data integrity during settling periods is improved, but more disk space is consumed by ECC sectors
Solution Approach 1:
The patent applies different ECC strengths to different zones based on local data stream characteristics. The system monitors the number of seeks (NS) over a predetermined time period and identifies when short data streams with frequent seeks are occurring. In these specific local situations, the system selects zones with more ECC sectors to ensure data integrity during head settling periods. For long data streams without frequent seeks, zones with fewer ECC sectors are selected, thus optimizing the balance between reliability and storage efficiency for different data access patterns.
Data Source
AI summary
A shingled magnetic recording disk drive with sector error correction code (ECC) has the disk recording surface divided into multiple zones. Each zone is assigned a sector-ECC strength, i.e., a unique number of ECC sectors associated with a block of data sectors. The zone in which data is to be written is determined from the time average of the position-error signal (PES), which is an indication of the track misregistration (TMR) and thus the current environmental condition to which the HDD is subjected.