Which I/O scheduler handles requests in a single FIFO queue order?

The noop I/O scheduler is designed to handle requests in a very simplistic manner, primarily treating I/O queue requests in a first-in, first-out (FIFO) sequence. This means that it processes requests in the exact order that they are received, without attempting to optimize the order of operations based on factors like latency or throughput.

The noop scheduler is particularly useful when dealing with devices that do not benefit from complex scheduling algorithms, such as flash-based storage systems, where traditional rotational optimizations are not applicable. It is lightweight and has minimal overhead, making it suitable for environments where simplicity and predictability of operations are prioritized.

In contrast, other schedulers such as deadline, cfq (Completely Fair Queuing), and bfq (Budget Fair Queuing) are designed to increase performance and efficiency by introducing algorithms that prioritize and reorder I/O requests based on various factors, such as how long they have waited or the type of workload being handled. These sophisticated schedulers aim to provide better responsiveness and improved resource utilization, which differentiates them from the straightforward FIFO approach of noop.