# 1.6 Exercises

1. If you have access to a UNIX or Linux system, access and read the manual pages for the utility iostat. Identify how you can use it to report the throughput of the disks in your system at regular intervals of five seconds. While iostat is running, initiate other activities (e.g., Web browsing, scrolling through files, listing directories) that use the disks. Compute the average throughput of the disk measured both in Kbytes/sec and in transactions (reads or writes) per second during a period of two minutes. Note that iostat also provides the average service time per transaction. Can you use this information to compute the utilization of each disk? Note that the utilization is the percentage of time that the disk is busy.

2. If you have access to a Windows NT, Windows 2000, or Windows XP system, learn how to use the Performance tool, which is part of the Administrative Tools. The Performance tool allows you to watch, in graph form, and log the values of many different counters for various system objects. One important system object is the Physical Disk and a relevant counter for that object is %Idle Time. Add the Physical Disk object and the %Idle Time counter to the metrics to be plotted by the Performance tool. Note that the utilization of the disk is given by 100 %Idle Time. Start various I/O intensive activities (e.g., opening MS Word documents, PDF files, images) and watch how the disk utilization varies.

3. An online trading system recorded the periods of time during which the service was down during the last two days and obtained the results shown in Table 1.2. What was the availability of the site during the two days?

##### Table 1.2. Online Trading Site Down Periods

Day

Start of Down Time

Duration of Down Time (min)

1

1:25 AM

12

1

7:01 AM

1

1

8:31 PM

5

2

2:15 AM

10

2

9:12 PM

6

4. Consider the same online trading site of the previous exercise and consider the down times for days 3 and 4 shown in Table 1.3. Compute the availability and compare your results with those of the previous exercise. How would you compare the two cases?

##### Table 1.3. Online Trading Site Down Periods

Day

Start of Down Time

Duration of Down Time (min)

3

9:35 AM

15

3

1:13 PM

2

4

10:31AM

3

4

2:15 PM

8

4

3:12 PM

6

5. Re-evaluate a software development project you were involved in and list the non-functional requirements related to performance and availability specified for the project. Explain how these requirements were addressed in each phase of the system life cycle.

Performance by Design: Computer Capacity Planning By Example
ISBN: 0130906735
EAN: 2147483647
Year: 2003
Pages: 166

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