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ep:labs:03:contents:tasks:ex1 [2020/07/30 20:39]
gheorghe.petre2608 [04. [20p] Monitor I/O with vmstat and 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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-==== 04. [20pMonitor I/O with vmstat and iostat ​==== +==== 01. [10pRotational delay - IOPS calculations ​====
-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 ===+<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:
  
-Write a script that reads the data into memory and generates a text file 500 times largerby concatenating ​the contents ​of the following novel {{:​ep:​labs:​olivertwist.txt|olivertwist.txt}} to itself. +  * **Rotational speed**. Measured in RPMmostly 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. 
-<solution -hidden+  * **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
-<​code>​ +  * **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). 
-if __name__ ​== '​__main__':​ +</note> 
-    text_file1 = open("​OliverTwist.txt",​ "​r"​) +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:  
-    text_file2 = open("​OliverTwistLarge.txt",​ "w+") +<​code>​average IOPS 1 / (average latency in ms average seek time in ms).
-    lines_file1 = text_file1.readlines() +
-    for x in range(0, 500)+
-    text_file2.writelines(lines_file1)+
 </​code>​ </​code>​
-</​solution>​ 
  
-=== [10p] Task B Monitoring behaviour ===+Let's calculate the Rotational Delay RD for a 10K RPM drive:
  
-Now we want to analyze what is happening with the I/O subsystem during an expensive operationMonitor ​the behavior of the system while running your script using **vmstat** and **iostat**.+  * Divide 10000 RPM by 60 seconds: **''​10000/​60 = 166 RPS''​** 
 +  * Convert 1 of 166 to decimal: **''​1/166 = 0.006 seconds per Rotation''​** 
 +  * Multiply ​the seconds per rotation by 1000 milliseconds (6 MS per rotation). 
 +  * Divide ​the total in half (RD is considered half a revolution around a disk): ​**''​6/​2 = 3 MS''​** 
 +  ​Add an average of 3 MS for seek time: **''​3 MS + 3 MS = 6 MS''​** 
 +  * Add 2 MS for latency (internal transfer): **''​6 MS + 2 MS = 8 MS''​** 
 +  * Divide 1000 MS by 8 MS per I/O: **''​1000/​8 = 125 IOPS''​**
  
-<note tip>​vmstat ​IO:+=== [10p] Task A Calculate rotational delay ===
  
-bi - column reports ​the number of blocks received ​(or “blocks in”from a disk per second.+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>​ 
 +As shown in the //"​Calculating IOs Per Second"//​ section: 
 +<​code>​ 
 +5400 / 60 = 90 RPS 
 +1/90 = 0.011 seconds per Rotation 
 +0.011 * 1000 = 11ms per Rotation 
 +11 / 2 = 5.5ms RD (Rotational Delay = half a revolution around ​a disk
 +add approx. 3ms seek time => 8.5ms 
 +add 2ms latency => 10.5ms 
 +Divide 1000ms by 10.5ms ​per I/O => approx95 IOPS 
 +</​code>​ 
 +</​solution>​
  
-bo - column reports the number of blocks sent (“blocks out”) to a disk per second. 
-</​note>​ 
  
  
ep/labs/03/contents/tasks/ex1.1596130781.txt.gz · Last modified: 2020/07/30 20:39 by gheorghe.petre2608
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