Scenario: An organization is deploying a new business application in their envir

Question

Scenario:
An organization is deploying a new business application in their environment. The new application requires 1TB of storage space for business and application data. During peak workload, the application is expected to generate 4,900 IOPS (I/O per second) with typical I/O size of 4KB. The available disks are 15,000 rpm drives with 100 GB capacities.

Other specifications of the drives are:

Average Seek time = 5 millisecond

Data transfer rate = 40MB/sec

Task:
Calculate the required number of disk drives that can meet both capacity and performance requirements for the new business application. Show your work, demonstrating how you arrived at the solution.

Explanation / Answer

Time Required to perform one I/O depends on DST that is Disk Service time.

DST = Average seek time + rotational latency + Data transfer time

NOW, Average seek time = 5ms , rotational latency = 1/2* of the time taken for full rotation = 1/2 * /(15000/60) = 2ms

Transferring of 4kb I/O takes 4KB/40MB/s = 0.1ms

Hence time required per I/O = 5+2+0.1= 7.1ms

Max number of IOPS disk can perform = 1/7.1ms = 140 IOPS

There should be a maximum of 70% utilization of disk controller for an acceptable response time.

Max number of IOPS disk can perform considering this is = 70% * 140 = 98

Application's performance requirement = 4900/98 = 50 disks

Application's capacity requirement is = 1TB/100GB = 10 disks

Ans) Number of disk required is the max of(50,10) that is 50 .

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