SMR Disk Drive Cache Verification Data Management
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Solution Overview
Problem
Shingled magnetic recording (SMR) hard disk drives face challenges in data integrity and storage efficiency due to the need for extensive verification processes and large media caches, especially when operating outside normal temperature ranges or when SMR bands are closed or reused.
Innovation Solution
Implementing a system where verification data stored in the conventional magnetic recording (CMR) region is invalidated under specific conditions such as SMR band closure, reuse, or completion, allowing for reduced media cache utilization and improved storage efficiency by managing verification data more dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If verification data is stored in the CMR region media cache to ensure data integrity in SMR regions, then data reliability is improved, but storage capacity and storage efficiency deteriorate
Solution Approach 1:
The system performs preliminary verification of SMR data by storing verification copies in the CMR media cache before the SMR bands are closed or reused. This allows data integrity to be confirmed in advance, and the verification data can be invalidated and removed from the media cache once verification is complete, freeing up storage capacity.
Solution Approach 2:
The system discards verification data from the CMR media cache after it has served its purpose of verifying SMR data integrity. The verification data is retained only temporarily until verification conditions are met (SMR band closure, reuse indication, or completion), at which point it is invalidated and removed, recovering storage capacity in the media cache.
2Reliability
If verification data is retained in the media cache until verification is complete, then data reliability is improved, but storage efficiency and productivity deteriorate
Solution Approach 1:
The system performs verification operations preliminarily while SMR bands are still open and accessible, rather than waiting until they are closed. This allows verification data to be validated earlier, reducing the duration that verification copies must be retained in the media cache and improving storage efficiency.
Solution Approach 2:
The system uses feedback signals from the host system regarding SMR band status (closure, reuse indication, or completion) to determine when verification data can be invalidated. This feedback mechanism allows the system to dynamically manage verification data retention, removing it as soon as verification conditions are satisfied, thereby improving storage efficiency while maintaining reliability.
3Reliability
If the media cache stores large quantities of unverified SMR data, then data integrity verification is improved, but device complexity and operational difficulty increase
Solution Approach 1:
The system applies different quality requirements to different portions of the media cache based on the status of SMR bands. Verification data is retained in the media cache only for specific SMR bands that require verification, rather than uniformly retaining all verification data. This localized approach reduces overall media cache complexity while maintaining verification capability for bands that need it.
Solution Approach 2:
The system systematically discards verification data from the media cache once the associated SMR bands are closed, marked for reuse, or verification is complete. This automated discarding process reduces media cache management complexity by eliminating the need for manual tracking and management of large quantities of verification data, while preserving verification capability when needed.
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 reduces the quantity of validation data stored in the CMR region, enhancing storage efficiency and performance by minimizing the media cache's workload and conserving storage capacity.
Implementation Method 1
A recently developed technology that has further increased the areal density of magnetic HDDs is shingled magnetic recording (SMR). In an HDD that employs SMR, groups of adjacent data tracks on a magnetic disk are written so as to overlap, and therefore overwrite, a portion of the previously written data track.
Implementation Method 2
This minimum width has prevented further decreases in written track width and areal density of HDDs, even though the width of a read head can be further reduced.
Data Source
AI summary
In a magnetic recording drive that includes a shingled magnetic recording (SMR) region and a conventional magnetic recording (CMR) region, the quantity of validation data that is stored by the CMR region is reduced. In the magnetic recording drive, verification data stored in the CMR region is invalidated under certain circumstances, including when an SMR band is closed, when an SMR band is indicated by a host to be reused, when an SMR band is indicated to be finished, and when a last data track of an SMR has data stored therein.