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ep:labs:03:contents:tasks:ex1 [2020/07/30 21:20] gheorghe.petre2608 [02. [5p] Iostat] |
ep:labs:03:contents:tasks:ex1 [2021/10/26 10:46] (current) radu.mantu [01. [10p] Rotational delay - IOPS calculations] |
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| - | ==== 01. [5p] Rotational delay - IOPS calculations ==== | + | ==== 01. [10p] Rotational delay - IOPS calculations ==== |
| - | + | ||
| - | === Good to know === | + | |
| + | <note tip> | ||
| Every disk in your storage system has a maximum theoretical IOPS value that is based on a formula. Disk performance and IOPS is based on three key factors: | Every disk in your storage system has a maximum theoretical IOPS value that is based on a formula. Disk performance and IOPS is based on three key factors: | ||
| - | * **Rotational speed**. Measured in RPM, mostly 7,200, 10,000 or 15,000 RPM. A higher rotational speed is associated with a higher performing disk. | + | * **Rotational speed**. Measured in RPM, mostly 7,200, 10,000 or 15,000 RPM. A higher rotational speed is associated with a higher-performing disk. |
| * **Average latency**. The time it takes for the sector of the disk being accessed to rotate into position under a read/write head. | * **Average latency**. The time it takes for the sector of the disk being accessed to rotate into position under a read/write head. | ||
| * **Average seek time**. The time (in ms) it takes for the hard drive’s read/write head to position itself over the track being read or written. | * **Average seek time**. The time (in ms) it takes for the hard drive’s read/write head to position itself over the track being read or written. | ||
| * **Average IOPS**: Divide 1 by the sum of the average latency in ms and the average seek time in ms (1 / (average latency in ms + average seek time in ms). | * **Average IOPS**: Divide 1 by the sum of the average latency in ms and the average seek time in ms (1 / (average latency in ms + average seek time in ms). | ||
| - | + | </note> | |
| - | To calculate the IOPS range, use this formula: Average IOPS: Divide 1 by the sum of the average latency in ms and the average seek time in ms (1 / (average latency in ms + average seek time in ms). | + | To calculate the **IOPS range** divide 1 by the sum of the average latency in ms and the average seek time in ms. The formula is: |
| + | <code>average IOPS = 1 / (average latency in ms + average seek time in ms). | ||
| + | </code> | ||
| Let's calculate the Rotational Delay - RD for a 10K RPM drive: | Let's calculate the Rotational Delay - RD for a 10K RPM drive: | ||
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| * Divide 1000 MS by 8 MS per I/O: **''1000/8 = 125 IOPS''** | * Divide 1000 MS by 8 MS per I/O: **''1000/8 = 125 IOPS''** | ||
| - | === IOPS calculations === | + | === [10p] Task A - Calculate rotational delay === |
| - | Calculate the rotational delay (RD) for a 5400 RPM drive. | + | Add in your archive the operations and the result you obtained. (Screenshot, picture of calculations made by hand on paper) |
| + | |||
| + | Calculate the Rotational Delay, and then the IOPS for a __5400 RPM drive__. | ||
| <solution -hidden> | <solution -hidden> | ||
| Line 38: | Line 41: | ||
| </code> | </code> | ||
| </solution> | </solution> | ||
| - | ==== 02. [5p] Iostat ==== | ||
| - | === Good to know === | ||
| - | |||
| - | <code> | ||
| - | #iostat [ -x for extended statistics, -d to display device stastistics only, -m for displaying r/w in MB/s ] | ||
| - | iostat -xdm | ||
| - | |||
| - | #iostat with -p for specific device statistics | ||
| - | iostat -xdm -p sda | ||
| - | </code> | ||
| - | |||
| - | === Monitoring the behaviour === | ||
| - | |||
| - | * Run //iostat -x 1 5//. | ||
| - | * Considering the last two outputs provided by the previous command, calculate the efficiency of IOPS for each of them. Does the amount of data written per I/O increase or decrease? | ||
| - | |||
| - | <note> | ||
| - | How to's | ||
| - | |||
| - | * Divide the kilobytes read (//rkB/s//) and written (//wkB/s//) per second by the reads per second (//r/s//) and the writes per second (//w/s//). | ||
| - | * If you happen to have quite a few [[https://en.wikipedia.org/wiki/Loop_device|loop devices]] in your **iostat** output, find out what they are exactly: | ||
| - | |||
| - | <code bash> | ||
| - | $ df -kh /dev/loop* | ||
| - | </code> | ||
| - | </note> | ||
| - | |||
| - | |||
| - | <solution -hidden> | ||
| - | The way to calculate the efficiency of IOPS is to divide the reads per second //(r/s)// and writes per second //(w/s)// by the kilobytes read //(rkB/s)// and written //(wkB/s)// per second. | ||
| - | |||
| - | Example: the amount of data written per I/O for ///dev/sda// increases during each iteration: | ||
| - | |||
| - | {{ :ep:labs:ep2017_l3_ex01.png?700 |}} | ||
| - | |||
| - | <code> | ||
| - | 53040/105 = 505KB per I/O | ||
| - | 71152/102 = 697KB per I/O | ||
| - | </code> | ||
| - | |||
| - | If everything is zero in iostat - perform some I/O operations... | ||
| - | </solution> | ||
| - | ==== 03. [5p] Iotop ==== | ||
| - | |||
| - | ==== 04. [20p] Monitor I/O with vmstat and iostat ==== | ||
| - | We said in the beginning that the disk I/O subsystems are the slowest part of any system. This is why the I/O monitoring is so important, maximizing the performance of the slowest part of a system resulting in an improvement of the performance of the entire system. | ||
| - | |||
| - | === [10p] Task A - Script === | ||
| - | |||
| - | Write a script that reads the data into memory and generates a text file 500 times larger, by concatenating the contents of the following novel {{:ep:labs:olivertwist.txt|olivertwist.txt}} to itself. | ||
| - | |||
| - | <solution -hidden> | ||
| - | <code> | ||
| - | if __name__ == '__main__': | ||
| - | text_file1 = open("OliverTwist.txt", "r") | ||
| - | text_file2 = open("OliverTwistLarge.txt", "w+") | ||
| - | lines_file1 = text_file1.readlines() | ||
| - | for x in range(0, 500): | ||
| - | text_file2.writelines(lines_file1) | ||
| - | </code> | ||
| - | </solution> | ||
| - | |||
| - | === [10p] Task B - Monitoring behaviour === | ||
| - | |||
| - | Now we want to analyze what is happening with the I/O subsystem during an expensive operation. Monitor the behavior of the system while running your script using **vmstat** and **iostat**. | ||
| - | |||
| - | <note tip> | ||
| - | Understanding vmstat IO section: | ||
| - | * **bi** - column reports the number of blocks received (or “blocks in”) from a disk per second. | ||
| - | |||
| - | * **bi** - column reports the number of blocks sent (“blocks out”) to a disk per second. | ||
| - | </note> | ||
