Integrating NAND flash devices onto servers

Abstract

Flash is a widely used storage device in portable mobile devices such as smart phones, digital cameras, and MP3 players. It provides high density and low power, properties that are appealing for other computing domains. In this paper, we examine its use in the server domain. Wear-out has the potential to limit the use of Flash in this domain. To seriously consider Flash in the server domain, architectural support must exist to address this lack of reliability. This paper first provides a survey of current and potential Flash usage models in a data center. We then advocate using Flash as an extended system memory usage model---OS managed disk cache---and describe the necessary architectural changes. Specifically we propose two key changes. The first improves performance and reliability by splitting Flash-based disk caches into separate read and write regions. The second improves reliability by employing a programmable Flash memory controller. It changes the error code strength (number of correctable bits) and the number of bits that a memory cell can store (cell density) in response to the demands of the application.