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Since the invention of the movable head disk, people have improved
I/O performance by intelligent scheduling of disk accesses. We have
applied these techniques to systems with large memories and potentially
long disk queues. By viewing the entire buffer cache as a write
buffer, we can improve disk bandwidth utilization by applying some
traditional disk scheduling techniques. We have analyzed these
techniques, which attempt to optimize head movement and guarantee
fairness in response time, in the presence of long disk queues. We
then propose two algorithms which take rotational latency into
account, achieving disk bandwidth utilizations of nearly four times
a simple first come first serve algorithm. One of these two
algorithms, a weighted shortest total time first, is particularly
applicable to a file server environment because it guarantees that
all requests get to disk within a specified time window.
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