Magnetic Disk Head Unload Control for Power-Loss Data Protection
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Solution Overview
Problem
Conventional magnetic disk devices face challenges in efficiently managing power loss scenarios, where user data in volatile memory may be lost if not properly written to the magnetic disk before power interruption.
Innovation Solution
The magnetic disk device incorporates a controller that calculates a power amount required for the unload operation of the magnetic head and sets a threshold value. When the amount of data in the volatile memory exceeds this threshold, the controller executes a first write operation to write data to the magnetic disk. In case of power loss, the controller uses back electromotive force to execute an unload operation and save data to a nonvolatile memory.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the controller frequently executes the first write operation to write data from volatile memory to magnetic disk, then data integrity during power loss is improved, but write performance deteriorates due to increased operation frequency
Solution Approach 1:
The controller dynamically adjusts the threshold value for triggering the first write operation based on the calculated power amount required for unload operation. By changing this parameter adaptively, the system optimizes the balance between data integrity and write performance, executing writes only when necessary rather than frequently or never.
Solution Approach 2:
The system transitions from a static write strategy to a dynamic one where the decision to execute the first write operation depends on real-time conditions. The controller continuously monitors the power amount required for unload operation and adjusts write operation frequency accordingly, making the system adaptive to changing operational states.
2Reliability
If the controller uses back electromotive force to execute unload operation and save data to nonvolatile memory during power loss, then data integrity is improved, but energy availability worsens due to power interruption
Solution Approach 1:
The controller converts the harmful effect of power loss into a beneficial resource by utilizing the back electromotive force generated during the unload operation. Instead of treating power interruption purely as a failure condition, the system harnesses the residual energy from motor deceleration to perform critical data saving operations to nonvolatile memory.
Solution Approach 2:
The system uses its own kinetic energy during the unload operation to power the critical data saving function. The back electromotive force generated by the first motor during deceleration serves the dual purpose of enabling the unload operation and providing power for saving data to nonvolatile memory, making the system self-sufficient during power loss events.
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 solution effectively reduces the frequency of the first write operation, thereby improving write performance while ensuring data integrity during power loss events by utilizing the back electromotive force for data saving.
Implementation Method 1
the controller executes the unload operation and saving of the second data to the nonvolatile memory by using power generated by a back electromotive force of the second motor
Data Source
AI summary
According to one embodiment, a controller of a magnetic disk device calculates a first power amount that is an amount of power required for an unload operation of a magnetic head based on a state of a VCM while the VCM is operating. The controller calculates a first set value based on the first power amount. When an amount of second data that is first data stored in a volatile memory and not yet written to a magnetic disk exceeds the first set value, the controller executes a first write operation of writing a part or all of the second data to the magnetic disk. When supply of power from outside is interrupted, the controller executes the unload operation and saving of the second data to a nonvolatile memory by using power generated by a back electromotive force of the second motor.