External DRAM adds memory to the SSD controller, with a size ratio of 1:1000 compared to the capacity. It has two main functions: caching data, merging it in memory, and then writing it to FLASH, and caching the FTL table ( Flash Translation Layer). External DRAM effectively enhances continuous write and random read/write performance.

For example: SSD Capacity: 1TB = External DRAM Size: 1GB

Why is it needed?

Performance Improvement: By storing frequently accessed data in the DRAM, the SSD controller can quickly retrieve this data without having to access the slower NAND flash memory. This significantly speeds up read operations and improves overall system performance.

Write Optimization: The DRAM allows the SSD controller to buffer data before writing it to the flash memory. This enables the controller to merge multiple small writes into larger blocks, which is more efficient for NAND flash memory that requires data to be written in larger blocks.

FTL Table Management: The FTL table, which maps logical addresses to physical addresses in the flash memory, is essential for data management. Caching a portion of the FTL table in the external DRAM enables the controller to quickly access and manage this mapping information, which is critical for data organization and retrieval.

Reducing Wear: The external DRAM can help reduce the number of writes directly to the NAND flash memory, as it can buffer data and optimize writes. This can extend the lifespan of the flash memory cells by reducing wear caused by frequent writes.

Handling Bursty Workloads: In scenarios with sudden bursts of read or write operations, the external DRAM can absorb and manage these bursts more effectively, providing smoother and more consistent performance.

Cost-Effective Solution: The use of an external DRAM allows for the integration of a smaller, more cost-effective NAND flash memory with higher-capacity, slower NAND flash, which provides a good balance of performance and cost.

Overall, the external DRAM is a crucial component that optimizes data access, enhances read and write performance, and improves the overall efficiency and longevity of the SSD. It is an essential feature in modern SSD controllers to deliver high-performance and reliable storage solutions.