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Archive for the ‘Performance’ Category

esxtop is a great tool that can provide a complete view of the storage profile (disk performance information between ESX and hardware), however when there are disk latency issues, it doesn’t give any further information such as what particular VM is suffering/causing from the latency. vscsiStats is the right tool to monitor the latency issues between the VM and ESX.

The following step-by-step process details the procedure for monitoring the VM SCSI counters. The vscsiStats command can be found in /usr/lib/vmware/bin and is not part of the path environment, which means that you either first change to this directory or refer to the full path every time you use the command: /usr/lib/vmware/bin/vscsiStats. This tool is subject to change based on the vSphere/ESX3.5 Build Number.

•    Login to any of the vSphere4 hosts using putty or any other SSH client that has access to the datastore on which you would like to monitor the statistics.
•    Make sure that /tmp has enough free space by using vdf –h command
•    Obtain the correct version of vscsiStats tool from VMware and copy the tool under /tmp either using WinSCP or any other SCP tool.
•    Type “vscsiStats –l” (it is lower case L) to list all the VMs that are running and determine the WorldID (a four digit number) of the VM for which you would like to measure the latency or any other histo_type (IOSize, Seek distance, Outstanding IOs etc.)
•    Once the WorldID is identified, type “vscsiStats –r” to reset the statistics, so it doesn’t keep any old data.
•    Type “vscsiStats –w XXXX –s” to start the collection of VM SCSI statistics for the VM we identified.
•    Wait for few seconds and type “vscsiStats –w XXXX –p latency”, which should display the latency statistics for WorldID XXXX. And verify the number for latency I/O statistics (you can safely ignore read and write I/O statistics) for each VMDK, which is identified with another four digit number. Please, make a note that the initial VMDK (C: drive) will start with a four digit number and the other consecutive VMDKs will be incremented by 1, for example if VMDK1 starts with 8227, then the next VMDK will start with 8228 and so on.
•    By default it stops after 30 minutes and remember that if this process restarts, it will reset all the counters, hence it is very important to save them to a csv file for which type “vscsiStats –w XXXX –p latency –c > /tmp/VMXXXX-vscsiStats.csv” and hit enter.
•    Now download the VMXXXX-vscsiStats.csv file onto a Windows workstation that has Microsoft Excel program using WinSCP or any other SCP tool.
•    Open the .csv file using Microsoft Excel program and expand the first two columns:
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Figure 1: vscsiStats Results
•    From the Figure 1, if you add all the rows under Frequency that have a value greater than 30000 (30 ms) and divide it with the mean value (as highlighted in pink), then that value will indicate the percentage of time the disk took an extraordinary latency for that particular VMDK.
•    Create a chart for the Frequency in the Legend Entries (Series) and Histogram Bucket Limit in the Horizontal (Category) Axis Labels.
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Figure 2: vscsiStats Results Chart
•    From the chart or from the csv, if you see any numbers higher than 30000 (30 milliseconds), for a considerable amount of time, then it indicates a bottleneck in the disk array for that particular VM.

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