Which Disk Scheduling Algorithm Suffers from Starvation

In this article, we will discuss disk scheduling algorithms that suffer from starvation, and the reasoning behind it.

Disk Scheduling Algorithms that suffers from Starvation

  1. Shortest Seek Time First ( SSTF )
  2. Priority Based Disk Scheduling

Shortest Seek Time First ( SSTF )

SSTF suffers from starvation.

SSTF satisfies the request which is at the shortest distance from the read-write head. Suppose the read-write head is currently at 50. The CPU requests to read from track 40 and 65. The read-write head would move from 50 to 40 because it is at a shorter distance from 50.

Let’s understand how it leads to starvation.

Suppose the read-write head is at track 50. The CPU sends a request to read from track 40 and 100. The read-write head will move towards track 40 since it is at the shortest distance. Now, suppose CPU keep sending read request near track 40. Due to this, the read-write head will never be able to read track 100 since all the new upcoming read requests will be at a shorter distance from the read-write head. The request for track 100 will starve.

Priority Based Disk Scheduling

Priority Based Disk Scheduling also suffers from starvation. It satisfies the request with higher priority first.

Let’s understand how it leads to starvation.

Suppose the system keeps sending requests for high priority reads. Due to this, any low priority requests will never be satisfied as the Disk Scheduler will be busy servicing higher priority requests. This leads to starvation.

Disk Scheduling Algorithms that do not suffers from Starvation

  1. First Come First Serve ( FCFS )
  2. SCAN ( Elevator Disk Scheduling )
  3. C-SCAN ( Circular Scan )
  4. LOOK
  5. C-LOOK ( Circular Look )

FCFS can never suffer from starvation because it services requests based on Arrival Time. The request which comes first is served first.

SCAN, LOOK also does not suffers from starvation as the read-write head keeps moving between first track and last track and services all the requests in between.

C-SCAN, C-LOOK do not suffer starvation as the read-write head keeps moving between request with minimum track number and request with maximum track number and services all the requests between them.

References

Disk Scheduling Algorithms

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