Head Velocity Derating for Data Storage Devices
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Data Storage Devices (DSDs) face an increased risk of head damage during Emergency Power Off (EPO) events due to the steepness of ramps in densely packed disk packs, which can cause head-slider flapping. Existing solutions that reduce the maximum speed of the head to prevent damage during EPO events compromise performance and increase the size of unused disk regions.
Innovation Solution
The implementation of a dynamic upper velocity limit reduction process for the head in Data Storage Devices, which adjusts the velocity limit based on multiple factors such as the starting position of the head, the direction of the seek, operating states, performance factors, and EPO history. This process ensures that the upper velocity limit is only reduced for longer seeks when the head has more momentum and is at a higher risk of damaging the ramp during an EPO event.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the maximum speed of the head is reduced to prevent damage during EPO events, then head damage risk is decreased, but performance decreases due to slower head movement
Solution Approach 1:
The patent implements dynamic velocity derating that adjusts the head's maximum velocity limit in real-time based on operational conditions. The system monitors factors such as current velocity, distance to ramp, disk rotation speed, and load characteristics, then dynamically modifies the velocity limit accordingly. This allows the head to operate at higher speeds during normal conditions while automatically reducing velocity only when EPO risk is detected, resolving the contradiction between maintaining high performance and preventing head damage.
Solution Approach 2:
The system changes the velocity parameter dynamically based on multiple conditional factors including current head velocity, distance to ramp position, disk rotation speed, and aerodynamic bearing conditions. By modifying the velocity limit parameter adaptively rather than using a fixed reduction, the system prevents head damage during EPO events while minimizing performance impact during normal operation.
2Reliability
If the maximum speed of the head is reduced to prevent damage during EPO events, then head damage risk is decreased, but the size of unused outer diameter region increases
Solution Approach 1:
The dynamic velocity derating system allows the head to maintain high velocities during normal operation, enabling the use of outer diameter regions that would otherwise be unusable with fixed velocity limitations. By only reducing velocity when specifically needed for EPO protection, the system recovers disk storage capacity and performance that would be lost with continuous velocity derating.
3Productivity
If the head moves faster during normal operation, then performance improves, but the risk of head-slider flapping during EPO events increases
Solution Approach 1:
The system applies preliminary anti-action by pre-calculating and preparing velocity derating parameters based on monitored conditions before an EPO event occurs. The control system continuously monitors disk rotation speed, head position, and aerodynamic conditions, and proactively adjusts velocity limits to prevent excessive momentum buildup that would cause head-slider flapping during ramp contact. This preliminary adjustment prevents the harmful effect rather than reacting after damage occurs.
Solution Approach 2:
The system uses feedback from multiple sensors monitoring head velocity, disk rotation speed, and position relative to the ramp to continuously adjust the velocity limit. This closed-loop control ensures the head operates at maximum safe velocity under current conditions, improving performance while preventing head-slider flapping by automatically reducing velocity when conditions indicate elevated EPO risk.
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 risk of head damage during EPO events while minimizing the performance penalty by only derating the upper velocity limit for specific conditions, allowing for faster seeks to other target locations and improving overall Input/Output Operations Per Second (IOPS) performance.
Implementation Method 1
The head is supported by a slider assembly that floats over the disk surface at approximately five nanometers due to an air bearing or lifting force of air caused by the rapid spinning of the disk
Data Source
AI summary
A Data Storage Device (DSD) includes a disk to store data, at least one head to read and write data on the disk, and a Voice Coil Motor (VCM) to move the at least one head over the disk. An upper velocity limit is reduced for moving the at least one head to perform a command to read or write data at a target location on the disk as a precautionary measure against damaging the at least one head during an Emergency Power Off (EPO) state. The upper velocity limit is reduced in response to the target location being in an Outer Diameter (OD) region of the disk, a direction needed to move the at least one head being in an Inner Diameter (ID) to OD direction, and a starting position being at least as radially far from an OD region position as a predetermined threshold.