What Systems Researchers Need to Know about NAND Flash

Flash memory has been an active topic of research in recent years, but hard information about the parameters and behavior of both flash chips and SSDs has been difficult to obtain for those outside of the industry. In this paper several misconceptions found in the literature are addressed, in order to enable future researchers to avoid some of the errors found in prior work.

We examine the following topics: flash device parameters such as page and erase block size, speed, and reliability, as well as flash translation layer (FTL) requirements and behavior under random and sequential I/O. We have endeavored to find public sources for our claims, and provide experimental evidence in several cases. In doing so, we provide previously unpublished results showing the viability of random writes on commodity SSDs when restricted to a sufficiently small portion of the logical address space.