Persistent Cache for Flash Memory FTL Mapping
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Solution Overview
Problem
Flash memory systems face performance degradation due to the slow access times of flash memory, particularly when retrieving portions of the Flash Translation Layer (FTL) mapping table, which is essential for translating logical block addresses to physical addresses.
Innovation Solution
Implementing a second, persistent cache that stores frequently accessed FTL map information, allowing for quicker access to mapping data and reducing the need for frequent accesses to slower flash memory.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If flash memory is used for storage, then non-volatile data retention is achieved, but access speed deteriorates
Solution Approach 1:
The patent divides the storage system into multiple components: flash memory for non-volatile storage and a persistent cache (separate memory region) for frequently accessed FTL mapping data. This segmentation allows each component to optimize for its specific function, with the cache providing fast access to critical mapping information while flash memory maintains data retention capabilities.
Solution Approach 2:
The persistent cache acts as an intermediary between the host system and the flash memory. Instead of directly accessing slow flash memory for every FTL mapping operation, the system uses the persistent cache as a buffer layer that stores hot mapping data, thereby mediating the access speed issue while preserving the non-volatile nature of flash memory.
2Duration of action of stationary object
If FTL mapping table is stored in flash memory, then data persistence is maintained, but random read performance deteriorates
Solution Approach 1:
The patent applies local quality by creating a persistent cache with specialized properties for storing FTL mapping data. This cache region has optimized characteristics for fast reading and updating of mapping entries, while the rest of the flash memory maintains its standard persistence characteristics. The mapping table is thus stored with different quality characteristics in different locations.
Solution Approach 2:
The system performs preliminary actions by pre-loading frequently accessed FTL mapping data into the persistent cache before actual read operations occur. This proactive caching strategy ensures that when random read operations need mapping information, the data is already available in the fast persistent cache rather than requiring slow flash memory access.
3Productivity
If persistent cache is implemented, then random read performance is improved, but device complexity increases
Solution Approach 1:
The persistent cache is designed to serve multiple functions: it acts as a cache for FTL mapping data, provides a buffer for write operations, and maintains persistence similar to flash memory. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in device complexity while still achieving improved random read performance.
Data Source
AI summary
Devices and techniques are disclosed herein for implementing, in addition to a first cache, a second, persistent cache in a memory system coupled to a host. The memory system can include flash memory. In certain examples, the first cache and the second cache are configured to store mapping information. In some examples, the mapping information of the second persistent cache is determined by the host using a persistence flag of memory requests provided to the memory system.