SSD Cache Internal Trim for Cold Data and Lower Write Amplification
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Solution Overview
Problem
Flash memory devices experience increased write amplification factor (WAF) due to frequent garbage collection operations, leading to deteriorated performance as they do not support overwriting, necessitating a solution to optimize data management and reduce WAF.
Innovation Solution
Implementing an internal trim operation in storage devices with nonvolatile memory cells, such as flash memories, to identify and delete 'cold data' using a least recently used (LRU) scheme when the valid data ratio exceeds a reference threshold, thereby reducing the need for garbage collection and lowering WAF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If garbage collection operations are performed frequently to secure storage space in flash memory, then storage space availability is improved, but write amplification factor increases and performance deteriorates
Solution Approach 1:
The patent applies preliminary action by performing trim operations on cold data before it becomes necessary to perform garbage collection. The memory controller identifies cold data (data not accessed for a predetermined period) and issues trim commands to erase it in advance, ensuring storage space is available without triggering frequent garbage collection operations that increase WAF.
Solution Approach 2:
The memory controller autonomously manages data lifecycle by automatically identifying cold data and performing trim operations without host intervention. The controller monitors data access patterns, determines which data has become cold based on access timestamps, and proactively erases it to maintain storage efficiency and reduce the burden on garbage collection mechanisms.
2Duration of action of stationary object
If data is retained in flash memory for extended periods, then data retention capability is improved, but storage space becomes insufficient and garbage collection frequency increases
Solution Approach 1:
The system performs preliminary trim operations on cold data before storage space becomes critical. By proactively erasing data that has not been accessed for a predetermined period, the system maintains storage space availability without requiring frequent garbage collection operations, thus resolving the contradiction between retaining data and managing storage space efficiently.
Solution Approach 2:
The patent changes the parameter of data validity by introducing a time-based criterion (predetermined period without access) to determine when data should be erased. This parameter change allows the system to dynamically manage storage space by erasing data based on its access pattern and age, balancing data retention with storage space availability.
3Quantity of substance
If copy and merge operations are performed on large amounts of data during garbage collection, then storage space is secured, but operational time and energy consumption increase
Solution Approach 1:
The system performs preliminary trim operations on cold data to erase it in advance before garbage collection is needed. This preliminary action reduces the amount of data that requires copying and merging during garbage collection, thereby reducing both the time and energy consumption of these operations while still securing storage space when needed.
Solution Approach 2:
The patent extracts cold data (data not accessed for a predetermined period) from the storage system and erases it through trim operations. By removing this data beforehand, the system reduces the volume of data that needs to be processed during garbage collection, minimizing the time and energy required for copy and merge operations.
Data Source
AI summary
A storage device includes a memory device and a solid state drive used as a cache memory for the memory device. The solid state drive includes a storage unit including a plurality of nonvolatile memory cells, a memory controller configured to control the storage unit, and a data management unit configured to manage pieces of data, stored in the storage unit, in order of less recent access time. The data management unit may set at least one of the pieces of data, stored in the storage unit, as cold data based on a data access point in time, and may send an internal trim command for the cold data to the memory controller when a valid data ratio of the storage unit is higher than a reference valid ratio. The memory controller may perform an internal trim operation on the cold data.