(A) Logging-based data management in a file system using flash memory

Abstract

Rapid advances in storage technology and the requirements of a new area such as mobile computing and embedded applications indicate that a new type of non-volatile solid state memory, flash memory, will replace conventional magnetic disks as a secondary storage. This storage organization enables system to have all data reside in fast memory and also can eliminate unnecessary data copy and movement between primary storage and secondary storage. In addition, it is expected to improve performance degradation caused by high disk access latency. Flash memory provides useful characteristics as a storage system, including non-volatility, in-system programmability, low power consumption, reasonable tolerance, and high density. Though it is possible to develop a file system using flash memory, this approach is not easy to implement due to flash memory``s deficiencies. The most complicated matter is that flash memory requires the need to erase blocks of memory before they are overwritten. The whole segment must be erased during data updates, which takes more time and needs lots of power. Furthermore, flash memory offers high access latency for write/erase operation, consuming a lot of power and provides the limited number of erase cycle in the lifetime of de-vice. The issues related to the design of a file system using flash memory can be categorized to two themes, i.e., how to overcome flash memory``s in-ability of in-place update and how to reduce the frequency of erase/write to flash memory. This thesis describes a new mechanism to overcome flash memory``s limitations in a file system using flash memory, offering non-in-place update scheme and a new cleaning policy. Firstly, we exploit two types of i-nodes which are allocated in separate flash areas and also introduce a delta logging method to efficiently utilize flash memory space. The separation of i-nodes copes with meta-data update that occupies the majority of write operations. During every update, the delta logg...