Flash File Systems

Posted by: Thom Denholm

Flash memory has established itself as the technology of choice for device data storage on embedded devices. The advantages it brings in terms of storage capacity, I/O throughput, power consumption and board space savings are significant. In 2007, flash memory was a $7.7 billion industry. Analysts predict a 23% growth of the flash memory market between 2007 and 2011; surpassing the history-making growth of DRAM ten times over. One of the barriers to flash memory adoption is its perceived complexity of integration into a product design. With the flash memory market branching to multiple product lines beyond traditional NAND and NOR devices, this perception, along with a concern about the reliability of flash, is becoming magnified. Basic flash management software can lessen the complexity of integration, and sophisticated flash software can ensure the optimum lifetime and reliability of a flash device. The challenges of integrating flash memory are broad, including operations from the seemingly simple - like reading, writing, and overwriting data - to the exceedingly complex - such as bad block management and wear-leveling. When flash memory is not accompanied by an intelligent software manager, the system will suffer from slow reads and writes, data corruption, and a short usable life. There has been a lot of interpretations for the term "Flash File System". Some consider it as the combination of flash management software and a block file system. For some it is just the flash management piece.   

Flash Driver: Basic software that provides rudimentary read/write access to flash; this software is often acquired from the chip provider, and is usually part-specific. ·

Flash Manager: In addition to the functionality of a flash driver, a flash manager also intelligently determines which part is being used, and handles it accordingly - whether it is NAND, NOR, or a fusion of the two (i.e. Samsung OneNAND, or Spansion ORNAND). Bad block management, wear-leveling, garbage collection, and error detection and correction are features that a flash manager provides. A flash manager may also be designed to take advantage of unique performance or technical characteristics a specific part provides. Flash managers are sometimes referred to as FTL (flash translation layers).

Flash File System: Contains the flash driver and the flash manager aspects, but also incorporates a file system that is designed for use with flash memory. In the way of performance optimizations, a flash file system includes a discard interface which ensures that erased blocks are immediately available for use by both the file system and the flash manager without additional queries to those blocks. Hope this post was useful in understanding the layers of flash management. In the next post in the series, we will look at various flash file systems for one of the most talked-about embedded OS - Linux.

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Comments (3)

  1. David Foster:
    Jan 20, 2012 at 09:31 AM

    the links to your pictures/diagrams don't work ... any chance you can fix that? Great articles btw. .. all the best, David F

  2. Michele Pike:
    Feb 24, 2012 at 10:21 AM

    These have been resolved, thanks for letting us know.

  3. Ramzes:
    Oct 10, 2012 at 08:17 PM

    interesting article Michele

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