A Flash-Memory Based File System

A flash memory device driver that supports a conventional UNIX file system transparently was designed. To avoid the limitations due to flash memory's restricted number of write cycles and its inability to be overwritten, this driver writes data to the flash memory system sequentially as a Log-structured File System (LFS) does and uses a cleaner to collect valid data blocks and reclaim invalid ones by erasing the corresponding flash memory regions. Measurements showed that the overhead of the cleaner has little effect on the performance of the prototype when utilization is low but that the effect becomes critical as the utilization gets higher, reducing the random write throughput from 222 Kbytes/s at 30% utilization to 40 Kbytes/s at 90% utilization. The performance of the prototype in the Andrew Benchmark test is roughly equivalent to that of the 4.4BSD Pageable Memory based File System (MFS).