11 myths about NAND Flash controllers

February 14, 2019 //By Damien Col
11 myths about NAND Flash controllers
Controllers are the game-changing components in NAND flash-based storage systems. While we talk about solid-state drives (SSDs) as an example that most people are familiar with in storage systems, the same controller- and system-related myths also apply to USB flash disks, eMMC modules, SD cards, or any other form of managed NAND device. It’s time to separate fact from fiction.

1. The latest flash generation is always the best.

New flash-memory generations hit the market with one mission: Squeeze more gigabytes of information into the costly silicon. As a result, the price per gigabyte decreases with newer generations of flash. However, this usually means fewer electrons are associated with one bit of information. Hence, the quality isn’t getting better per se. It’s becoming more complex to manage. While this isn’t critical for the consumer market, where quality and reliability are second to price, the fact that the latest NAND flashes can be used in highly demanding applications is due to the close collaboration of flash and controller vendors.


2. Performance doesn’t depend on capacity.

SLC, MLC, and TLC NAND flash memories.

Flash-array write and read times are slower than the system performance. To reach a certain performance, controllers need to interleave read and write operations, meaning access different flash arrays at the same time. Especially for write performance, it’s necessary to connect several flashes and hence provide higher capacity. On the other hand, newer flashes increase the per-die capacity so that an SSD based on a newer flash technology may be slower at the same overall capacity.


3. When you compare the performance of different SSDs, bigger is always better.

Datasheets usually promote attractive performance and often refer to the burst speed of the interface. However, looking at the system, often the performance bottleneck of the system is either in the controller or limited by the flash technology. Most significantly, while the fresh-out-of-the-box performance is great, performance, especially random write speed, deteriorates as soon as the drive is filled.

Many systems are optimized to look outstanding new with popular benchmark programs. However, depending on your usage, the real experience can differ significantly. Using cheap flashes and cheap controllers never has a performance benefit in the long run.

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