A potential issue with the SSTF disk scheduling algorithm is:

Question

BlackTom AI · Accepted Answer

When evaluating a disk scheduling algorithm like SSTF, it's important to distinguish what aspects it optimizes and what drawbacks it can introduce.
Option a: 'Starvation of requests far from the head' describes a well-known issue with SSTF. Because SSTF always services the pending request closest to the current head position, requests that are far away from the head may be left waiting for a very long time if newer nearby requests keep arriving. This creates a potential starvation problem for distant I/O requests.
Option b: 'Low throughput' would suggest that the algorithm cannot achieve high overall I/O processing rates. In practice, SSTF tends to improve throughput relative to simple FCFS by reducing seek times on average, since seeks are shorter on average when choosing the nearest request. So low throughput is not typically cited as the primary drawback of SSTF.
Option c: 'High rotational latency' concerns the time wasted waiting for the disk to rotate to the correct sector. SSTF does not directly influence rotational latency, because rotational latency is determined by the disk’s rotational speed and the position of the requested sector, not by the order in which requests are served. Therefore, SSTF does not inherently cause high rotational latency.
Option d: 'Fairness to all requests' touches on the overall equity of service, which is related to starvation. While SSTF can be efficient, it does compromise fairness because some requests may be favored over others depending on their proximity to the current head position. This ties back to the same fundamental issue highlighted in option a, though it is phrased as a broader fairness concern rather than the specific starvation outcome.
In assessing these choices, the core concept is that SSTF’s proximity-based selection can cause distant requests to wait indefinitely in the presence of a continuous stream of nearby requests, while not necessarily minimizing rotational latency, and it tends to improve throughput rather than degrade it. The misfit options either misunderstand SSTF’s impact on throughput, ignore the proximity-driven behavior affecting fairness, or misattribute latency aspects that SSTF does not directly control.

System Software and Computing Concepts (032025-NHM)

A potential issue with the SSTF disk scheduling algorithm is:

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Which disk scheduling algorithm might lead to a "sweeping" effect where requests are serviced in a patterned manner across the disk?

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