File System Performance: Techniques and Optimizations

This lecture discusses file system performance, focusing on key metrics such as I/O operations, speed, and the impact on programs. The instructor defines performance and introduces three main techniques to improve it: caching, batching, and adding levels of indirection. Caching eliminates unnecessary operations, while batching groups operations to enhance throughput. The lecture explains the importance of the block cache and how it allows the operating system to avoid repeated disk I/O by storing frequently accessed data in memory. The concept of disk fragmentation is introduced, emphasizing the need for consecutive block access to minimize latency. The instructor also covers the strategy of delaying write operations to optimize performance, highlighting the risks of data loss during system crashes. Modern file systems, including log-structured file systems, are discussed, showcasing how they leverage these techniques for efficient metadata operations. The lecture concludes with an alternative approach of bypassing the kernel for direct disk access, commonly used in high-performance database systems.