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Coding techniques to extend the lifetime of non-volatile memories, including Flash memory and solid-state drives, in computer systems

Value proposition

Solid state disks (SSD) have been gaining ground for replacing hard disk drives (HDDs) as the storage medium of choice for both consumer and enterprise applications. Flash SSDs are popular because of their speed, reliability, and availability. However, one of Flash SSD's issues is wear out. Wear out refers to the fact that an SSD can only support a limited number of writes (and erases) before cells fail. This shortcoming can be magnified by patterns of writing data that concentrate writes on a small number of cells in a given device. Accordingly, extending the operating life of Flash memory is an area of ongoing research in order for SSDs to continue to make inroads in replacing HDDs.

Technology

A novel Duke invention presents a solution to this problem. It is systems and methods for increasing the number of writes to a page of non-volatile memory before the page must be erased. Instead of writing a dataword directly to memory, a codeword is written to the memory location. This codeword is selected to minimize overwrite and to maximize the spread of wear across memory cells. The coset coding is also integrated with error correction encoding. Once the previous state of a page is determined, a coset representative is selected based on the maximization of the number of writes to the page before erasing. The extends the life of the Flash and decreases the likelihood of degradation which could lead to errors in the system performance. It is shown that page write efficiencies of over 85% and lifetime gains of over 500% are possible with only modest encoding and decoding complexity. These methods and techniques can be carried out in any system in order to extend the lifetime of the memory.

Applications

Non-volatile memory

Advantages

  • Maximize number of writes
  • Reduce frequency of a page must be erased
  • Improve the lifetime for SSDs

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