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May 15th, 2011 18:00

ISM question on disk utilization

Can someone explain how these calculations are done ?

Consider a disk I/O system in which an I/O request arrives at a rate of 100 IOPS and the service time is 4 ms.

What is the utilization?

A. 40%

B. 10%

C. 80%

D. 4%

Answer:

A

5 Practitioner

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274.2K Posts

May 17th, 2011 21:00

Formula for this problem is:

U = Rs/Ra

Where: U is utilization, Rs is the service time, and Ra is the average inter-arrival time.

Given:

I/O request arrives = a = 100 IOPS

service time = Rs = 4 ms

Ra = 1/a = 10 ms

U = Rs/Ra = 4/10 = 0.8 or 40 %

16 Posts

May 18th, 2011 08:00

Rs: service time is 4ms = 4/1000 sec

a:  arrive rate of 100 IOPS

U= a * Rs

   =100 * (4/1000)  = 0.4

So the Utilization percentage would be 40%

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