SMR Magnetic Disk Shared Read Buffer Control
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Solution Overview
Problem
In Shingled Magnetic Recording (SMR) technology, the narrow track pitch leads to accidental erasure of existing data during new data writing, necessitating sequential writing and complex data management to prevent data destruction during updates, which inefficiently doubles the read operations for both update and host read processes.
Innovation Solution
A magnetic disk apparatus with a control circuit that executes a shared read operation, where band data targeted for update is read once and stored in a buffer memory, allowing for simultaneous update and transmission to the host, reducing redundant reads by using separate buffer areas for host read and update processes, and enabling parallel access with multiple actuator systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sequential write is used to prevent accidental erase of existing data in SMR, then data safety is improved, but write complexity and time are worsened
Solution Approach 1:
The magnetic disk is divided into multiple bands in the radial direction, and each band is further divided into multiple tracks. The control circuit manages write operations by sequentially processing bands and tracks within each band, segmenting the complex write task into manageable units to prevent data erosion while maintaining organization.
Solution Approach 2:
Before performing a write operation, the control circuit determines the write destination by identifying the first band and first track based on the data address. This preliminary determination establishes the writing sequence in advance, ensuring that data is written in the correct order without erasing existing data.
2Ease of manufacture
If separate read operations are executed for update and host read processes, then data management is simplified, but read efficiency is worsened due to redundant reads
Solution Approach 1:
The control circuit merges the update read process and the host read process into a single shared read operation. When data is read for update, the control circuit simultaneously makes this data available to the host if needed, combining two separate read operations into one to eliminate redundancy and improve efficiency.
Solution Approach 2:
The buffer memory is designed to serve multiple functions: it stores data read for update operations, and simultaneously provides this data to the host for read requests. This multi-functional use of the buffer memory eliminates the need for separate read operations and improves overall read efficiency.
3Reliability
If band data is read and stored in buffer memory for update, then update reliability is improved, but buffer memory usage and processing complexity are worsened
Solution Approach 1:
The buffer memory is divided into multiple buffer areas, with at least one buffer area dedicated to storing band data read for update operations. This segmentation isolates update-related data from other data, ensuring update reliability while organizing the complexity of data management in a structured manner.
4Quantity of substance
If track pitch is narrowed in SMR to improve recording density, then storage capacity is improved, but risk of accidental data erase increases
Solution Approach 1:
The magnetic disk is divided into multiple bands in the radial direction, with each band containing multiple tracks. The control circuit manages write operations by sequentially processing bands and tracks, creating a structured approach that prevents accidental data erosion even when track pitch is narrow.
Solution Approach 2:
Before performing a write operation, the control circuit determines the write destination by identifying the first band and first track based on the data address. This preliminary determination establishes the writing sequence in advance, ensuring that data is written in the correct order without erasing existing data.
Data Source
AI summary
According to one embodiment, a magnetic disk apparatus is provided with a magnetic disk, a buffer memory, and a control circuit. The magnetic disk has plural bands, each of which is a storage area in which data is written by the method of SMR. The control circuit receives a read request from outside. If the data requested to be read is first data of an update target stored in a first band among plural bands, the control circuit reads the first data from the first band, stores the first data in a buffer memory, and updates the first data in the buffer memory. Then, the control circuit transmits the first data in the buffer memory to the outside and writes the first data in the buffer memory to one of the plural bands.