SMR Disk Controller Data Access via Parity Recovery
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Solution Overview
Problem
Disk drives face long data access times due to mechanical latency when moving actuators over large distances, and Shingled Magnetic Recording (SMR) introduces challenges with track overlap affecting data integrity and sequential writing, complicating pre-read and post-read operations.
Innovation Solution
The implementation of a disk drive system that uses a controller with a logical-to-physical translation table and error correcting codes like LDPC to manage data access, determine data validity, and optimize caching policies, allowing for efficient data storage and retrieval in SMR environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If shingled magnetic recording is used to increase storage density, then storage capacity increases, but data access complexity increases due to track overlap and sequential writing requirements
Solution Approach 1:
A translation layer is introduced between the host and the SMR disk to handle the complexity of shingled magnetic recording. This translation layer manages track overlap, handles sequential writing constraints, and provides a simplified interface to the host system, thereby resolving the contradiction between increased storage density and data access complexity
Solution Approach 2:
Data is pre-processed and organized before being written to the SMR disk. The system performs preliminary actions such as determining valid data regions, managing translation tables, and preparing data in the correct sequence for shingled recording, which simplifies the actual write operations and reduces access complexity
2Loss of time
If pre-read and post-read operations are implemented to reduce mechanical latency, then data access time improves, but data validity becomes difficult to determine in SMR environments
Solution Approach 1:
The system implements feedback mechanisms through translation tables that track the validity of data on the SMR disk. When pre-read or post-read operations retrieve data, the translation layer provides feedback about whether the data is still valid (i.e., not overwritten by sequential writing), allowing the system to safely use cached data without compromising reliability
Solution Approach 2:
The translation layer acts as an intermediary that verifies data validity before allowing pre-read or post-read data to be used. It checks whether data in cached sectors is still valid according to the translation table, thereby resolving the contradiction between reducing access time through pre-read operations and maintaining data validity in SMR environments
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 mechanical latency and improves data access times by efficiently managing data validity and caching in SMR systems, maintaining data integrity while increasing storage density.
Implementation Method 1
The HSA can be attached to an actuator that is typically moved by a voice coil motor (VCM)
Implementation Method 2
heads to read data from the disks and/or to write data on the disks
Implementation Method 3
heads to read data from the disks and/or to write data on the disks
Data Source
AI summary
Methods and apparatus for facilitating pre-read and/or post-read operations of a disk drive. A write command is received including a logical block address (LBA) for user data in the write command. Parity data for correcting the user data is generated by encoding the LBA with the user data. The parity data is written on a disk of the disk drive with the user data so that the LBA can be recovered using the parity data when read from the disk. When a read command is received by the disk drive, requested user data is read from a first sector. User data and parity data is read from a second sector adjacent the first sector. The parity data is used to recover an LBA for the second sector and it is determined whether to store the user data read from the second sector based on the recovered LBA.