PPT Slide

Disk scheduling policies

Name

Description

Characteristic

Selection according to requestor:

RSS

random scheduling

for analysis only

FIFO

first-in, first-out

fairest of them all

PRI

priority by process

control not based on disk queue management

LIFO

last-in, first-out

maximize locality and resource utilization

Selection according to requested item:

SSTF

shortest service first

high use, small queues

SCAN

back and forth over disk

better service distribution

C-SCAN

one way with fast return

lower service variability

N-step-SCAN

SCAN of N records at a time

service guarantee

FSCAN

N-step-SCAN with N= queue size

load sensitive

OS maintains a queue of requests for each I/O device

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