SSD Garbage Collection Control via Load Threshold Monitoring
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Solution Overview
Problem
In storage devices like SSDs using NAND flash memory, garbage collection processes interrupt data writing/reading operations and can lead to system instability and unnecessary wear, as they are typically executed during idle times without considering the device's workload.
Innovation Solution
The storage device itself determines its idle state based on threshold values related to command queues and data sizes, and stops or resumes garbage collection accordingly to avoid interfering with active operations, ensuring that garbage collection is not executed during peak usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If garbage collection is executed during idle times, then memory areas with unnecessary data are reused, but data writing/reading operations are interrupted and system stability deteriorates
Solution Approach 1:
The garbage collection execution decision is made dynamic by continuously monitoring the loaded state of the storage device. The system adapts garbage collection execution based on real-time workload conditions, switching between executing and suspending garbage collection according to whether the device is in a high or low loaded state, thereby resolving the contradiction between system stability and operation continuity
Solution Approach 2:
The system implements a feedback mechanism where the loaded state (command queue depth, data transfer rate) is continuously monitored and used to control garbage collection execution. When the loaded state exceeds a threshold, garbage collection is suspended; when below the threshold, it is executed, creating a closed-loop control system that maintains both stability and productivity
2Productivity
If garbage collection is executed frequently, then memory reuse efficiency is improved, but device wear increases
Solution Approach 1:
The system changes the execution parameter of garbage collection from a fixed schedule to a condition-based parameter. By monitoring the loaded state and executing garbage collection only when the loaded state is below a threshold, the system optimizes the balance between memory reuse efficiency and device wear, extending device lifespan while maintaining productivity
3Productivity
If garbage collection is suspended during high workload, then data writing/reading operation continuity is maintained, but memory area reuse is delayed
Solution Approach 1:
The system implements periodic monitoring of the loaded state and executes garbage collection in periodic intervals when conditions permit. This periodic action ensures that memory reuse occurs regularly without continuously interrupting data operations, balancing operation continuity with memory reuse timing
Data Source
AI summary
According to one embodiment, a storage device includes a nonvolatile memory and a controller. The nonvolatile memory cannot overwrite data written in a memory area. The controller controls writing/reading of data to/from the nonvolatile memory in response to a request from a host device. The controller includes a garbage collection processor and a garbage collection controller. The garbage collection processor executes garbage collection to reuse a memory area on the nonvolatile memory in which unnecessary data remain. The garbage collection controller stops the garbage collection executed by the garbage collection processor when the storage device is in a loaded state equal to or less than a threshold value.