How to use Performance Monitoring (Perfmon.msc) to investigate slow disk performance (DSSU)

Performance Monitoring is a diagnostic tool provided inWindows. This tool is useful in checking if there is something going on with theserver during off peak hours and extensive logging through performance logs canhelp accumulate accurate information regarding bottleneck elements on theproblem servers disk.


Perform the following steps on the targetserver (NetBackup Media Server holding the DSSU) that has performance issueswriting data to a disk.

1. Open "Perfmon.msc" from the Run dialog. ExpandPerformance Logs and Alerts and right click Counter Logs and then click NewLog Settings, as shown in the figurebelow.

 

2. In theresulting dialog box type the name of the log setting that needs to be appliedon the problem server e.g. NBU-DSSU as shown below

 


3. Select counters to be monitored by clicking Add Counter on LogProperties dialog box. The counters that should be helpful are listed in a tablebelow.

 

List of counters thatwill help investigate the state of thedisk:  

 

Performance Object	Corresponding Counters to Add
Physical Disk	%Idle Time - This counter reports the percentage of time during the sample interval that the disk was idle.
Physical Disk	Disk Read Bytes/Sec - This is the rate at which bytes are transferred from the disk during read operations.
Physical Disk	Disk Write Bytes/Sec - This is the rate at which bytes are transferred to the disk during write operations.
Physical Disk	Split I/O per sec - This counter reports the rate at which I/Os to the disk were split into multiple I/Os. A split I/O may result from requesting data of a size that is too large to fit into a single I/O or that the disk is fragmented.

4. Once allthe relevant counters are added on the General Tab set the interval at which asample should be collected to 2 seconds. There is no harm in selecting theinterval as 1 second; it depends on how long it is required to log the data.Logging for longer periods with a minimum interval may cause large log files tobe generated.

 

5. Click onthe Log Files tab and select Log File Type as Text File (Comma Delimited).Nothing else changes here.

 


6. Most important of all the steps is selecting the right scheduleto check the disk activity at a stretch before the backup starts. Disk I/O andprocessor utilization will be high when the server runs into the backup scheduleso it is not suggested setting up a performance logging schedule that spansacross the entire backup time frame. Best recommended setting is to startperformance monitoring 10 minutes before the backup job starts (so that we cancapture disk idle times) and end it when its 20 minutes since the server isbeing backed up. This helps in providing a broader view of the disks performancebefore and after the backup has just started. For e.g. If a backup job starts at7:00PM start performance monitoring at 6:50PM and end it at 7:20PM on the sameday.

 


7. Oncethe schedule is set, click Apply and then click OK. An entry of the loggingelement is listed in the performance monitor as shown below.
 

8. Once thelogging is complete generate an HTML file to obtain the graphical informationabout the logging achieved so far by right clicking on the logging element andselecting ' Save Settings As'

 


9. Open the HTML file in Internet Explorer. A prompt to allowinteractions with an ActiveX control will appear on the browser screen. Allowthe interaction to occur. The HTML file runs the local Perfmon.msc as an ActiveXcontrol in the browser and loads the logged values from the CSV file to generatea static view of the values the counters have put forward, while logging thedata. If you want to view the graphical display on another machine export theHTML file and the corresponding CSV file. Place the CSV file in the C:\Perflogspath and then open the HTML file. To view the values according to specific timeframes within the logging schedule right click on the graph and clickProperties. On the Source tab move the scrolling slider to the desired timeframe and a corresponding Graph will begenerated.

 


 


 



Hereis how we would calculate how much data a disk can write per hour.

In theabove example the disk is writing around 1801341 Bytes/Sec i.e around 1.71MB /sec ; so

1.71MB x 60 seconds = 102.6MB / Minute
102.6MB x 60 minutes =6156MB / Hour

That's around 6GB per hour. We have a slow disk. Comparethe backup speed with the disk write bytes /sec