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--- ep:labs:03:contents:tasks:ex2 [2019/10/13 18:01]
emilian.radoi
+++ ep:labs:03:contents:tasks:ex2 [2022/09/13 12:59] (current)
radu.mantu [02. [30p] iostat & iotop]
@@ Line 1: / Line 1: @@
-==== 02. [10p] Monitor I/O with vmstat and iostat ====
+==== 02. [30p] iostat & iotop ====
-=== [5p] Generate a script to determine the occurences of the words ===
+=== [15p] Task A - Monitoring the behaviour with Iostat ===
+<note tip>
+Parameteres for iostat:
+    * -x for extended statistics
+    * -d to display device stastistics only
+    * -m for displaying r/w in MB/s
+<code bash>
+$ iostat -xdm
+</code>
+Use iostat with -p for specific device statistics:
+<code bash>
+$ iostat -xdm -p sda
+</code>
+</note>
-  * Write a script for determining the number of occurrences of the words //"not"//, //"yes"// and //"course"// in the large text file that you generated earlier.
+  * 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**?
-=== [5p] Monitoring the behaviour ===
+Add in your archive screenshot or pictures of the operations and the result you obtained, also showing the output of iostat from which you took the values.
-  * Monitor the behaviour of the system while running your code (//vmstat//, //iostat//).
-Hint:
+<note>
+How to do:
+  * 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>
-  * [[https://stackoverflow.com/questions/17268958/finding-occurrences-of-a-word-in-a-string-in-python-3|Finding occurrences of a word in a string in python 3]]
-  * [[https://stackoverflow.com/questions/8369219/how-do-i-read-a-text-file-into-a-string-variable-in-python|How to read a text file into a string variable and strip newlines?]]
 <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>
-import re
+/105 = 505KB per I/O
-if __name__ == '__main__':
+/102 = 697KB per I/O
-	word1 = "not"
+</code>
-	word2 = "yes"
-	word3 = "course"
-	text_file = open("OliverTwistLarge.txt", "r")
-	text_string = text_file.read().replace('\n', ' ')
-	word1_count = sum(1 for _ in re.finditer(r'\b%s\b' % re.escape(word1), text_string))
-	word2_count = sum(1 for _ in re.finditer(r'\b%s\b' % re.escape(word2), text_string))
-	word3_count = sum(1 for _ in re.finditer(r'\b%s\b' % re.escape(word3), text_string))
-	print 'The word <%s> occurs %d times'%(word1, word1_count)
+If everything is zero in iostat - perform some I/O operations...
-	print 'The word <%s> occurs %d times'%(word2, word2_count)
+</solution>
-	print 'The word <%s> occurs %d times'%(word3, word3_count)
+=== [15p] Task B - Monitoring the behaviour with Iotop ===
+<note tip>
+**Iotop** is an utility similar to top command, that interfaces with the kernel to provide per-thread/process I/O usage statistics.
+<code>
+Debian/Ubuntu Linux install iotop
+$ sudo apt-get install iotop
+How to use iotop command
+$ sudo iotop OR $ iotop
 </code>
+Supported options by iotop command:
+| **Options** | **Description** ^^
+| --version | show program’s version number and exit ||
+| -h, --help	| show this help message and exit ||
+| -o, --only	| only show processes or threads actually doing I/O ||
+| -b, --batch	| non-interactive mode ||
+| -n NUM, --iter=NUM	| number of iterations before ending [infinite] ||
+| -d SEC, --delay=SEC	| delay between iterations [1 second] ||
+| -p PID, --pid=PID	| processes/threads to monitor [all] ||
+| -u USER, --user=USER	| users to monitor [all] ||
+| -P, --processes	| only show processes, not all threads ||
+| -a, --accumulated	| show accumulated I/O instead of bandwidth ||
+| -k, --kilobytes	| use kilobytes instead of a human friendly unit ||
+| -t, --time	| add a timestamp on each line (implies –batch) ||
+| -q, --quiet	| suppress some lines of header (implies –batch) ||
+</note>
+  * Run iotop (install it if you do not already have it) in a separate shell showing only processes or threads actually doing I/O.
+  * Inspect the script code ({{:ep:laboratoare:dummy.sh|dummy.sh}}) to see what it does.
+  * Monitor the behaviour of the system with iotop while running the script.
+  * Identify the PID and PPID of the process running the dummy script and kill the process using command line from another shell (sending SIGINT signal to both parent & child processes).
+  * Hint - [[https://superuser.com/questions/150117/how-to-get-parent-pid-of-a-given-process-in-gnu-linux-from-command-line|How to get parent PID of a given process in GNU/Linux from command line?]]
+Provide a screenshot in which it shows the iotop with only the active processes and one of them being the running script. Then another screenshot after you succeeded to kill it.
+<solution -hidden>
+{{:ep:laboratoare:lab3-ex4.png?600}}
+**dd** performs disk writes... wow! Reason why there are no disk reads is because it uses pseudo-files from **devtmpfs** that don't record these statistics. Also, **tmpfs** are not disks :p
+Find PPID from PID: ps -o ppid= -p PID
+Send SIGINT signal: kill -SIGINT PID,PPID
 </solution>

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ep/labs/03/contents/tasks/ex2.1570978884.txt.gz · Last modified: 2019/10/13 18:01 by emilian.radoi

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