Host-Guided UFS Unmap Control for Garbage Collection Stability
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Solution Overview
Problem
The difference between valid data recognized by a host and real valid data in a storage device leads to degraded performance in storage systems, particularly in semiconductor memory devices, due to increased garbage collection costs and emergency garbage collections when the device-filled-ratio is not accurately managed.
Innovation Solution
The host proactively issues a discard command by querying and checking the device-filled-ratio of the storage device's data storage space, using UFS protocol information units, to prevent unnecessary garbage collection and maintain efficient storage operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the host does not query the device-filled-ratio, then the storage device operates autonomously, but the difference between valid data recognized by host and real valid data increases, leading to degraded performance
Solution Approach 1:
The host queries the device-filled-ratio from the storage device and uses this feedback information to issue unmap commands for logical block addresses that are no longer valid. This closed-loop feedback mechanism ensures the host's view of valid data matches the device's actual state, preventing performance degradation from data validity inconsistencies.
Solution Approach 2:
The host proactively queries the device-filled-ratio before performing write operations. By obtaining advance knowledge of which logical block addresses are no longer valid, the host can issue unmap commands in advance, allowing the storage device to prepare for garbage collection and avoid emergency collections during active operations.
2Loss of energy
If the host issues unmap commands based on device-filled-ratio, then garbage collection costs are reduced, but additional communication overhead is introduced between host and device
Solution Approach 1:
The query mechanism uses existing UFS protocol information units (UPIUs) that already serve multiple functions in the storage system. By repurposing these standardized communication structures for device-filled-ratio queries, the solution avoids introducing entirely new communication protocols, thereby reducing overall system complexity while enabling efficient garbage collection management.
3Ease of operation
If the device-filled-ratio is not accurately managed, then the storage device can operate with simpler internal logic, but emergency garbage collections occur, degrading storage operations
Solution Approach 1:
The storage device autonomously calculates and reports its own device-filled-ratio to the host without requiring complex external management. This self-service approach allows the device to maintain accurate internal state information while keeping the host informed, enabling simple yet effective coordination for garbage collection without introducing complex dual-management logic.
Data Source
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AI summary
There is provided a method of operating a storage system that includes a host and a storage device. According to the method, device-filled-ratio of a storage space of a plurality of nonvolatile memory devices in the storage device is queried by the host to the storage device, calculated device-filled-ratio is transmitted, by a storage controller that controls the plurality of nonvolatile memory devices, to the host in response to the querying, an unmap command and target logical block addresses are transmitted, by the host, to the storage device based on the calculated device-filled-ratio, and physical block addresses corresponding to the target logical block addresses are deallocated, by the storage device, in response to the unmap command.