(A) Scalable real-time NAND flash file system for mobile multimedia devices

Abstract

Mobile multimedia devices have become a primary product in the mobile embedded device market. Along with the mobile multimedia devices, NAND flash memory has become popular due to its outstanding characteristics such as small size, light weight, high density, low power dissipation, and solid state reliability. However, due to NAND flash’s erase-before-write and bulk-erase characteristics, NAND flash memory is often used with flash-aware file systems. In designing a flash file system for mobile multimedia devices, we confront two considerable issues. First one is scalability. As the computational resources such as memory and a processor in mobile devices is strictly limited because power budget and the mass production cost, the flash file system should be designed to use limited memory while supporting large scale flash memory. The other issue is real-time performance guarantee for recording. Although this issue was addressed in numerous disk-based systems, distinct problems arise due to the difference of the characteristics of NAND flash compared to those of disks. In this thesis, we design and implement scalable flash file systems, called ScaleFFS and RTFFS, for mobile multimedia devices. ScaleFFS mainly addresses the scalability problem of conventional flash file systems related to the memory consumption and mount time. To resolve the problem, we borrow the basic architecture of LFS and modify data structures and policies for NAND flash memory. RTFFS is completely redesigned to provide the real-time performance guarantee as well as high scalability. To achieve this, we first design an index structure which has a constant update cost by combining μ-Tree and extent-based inode pages. Second, we suggest a space management scheme to alleviate the garbage collection cost of writing multimedia data. In this scheme, two different allocation units are used according to the type of data. For multimedia files, the unit is a block, and it is exclusively assigned to th...