VDI Load Testing: When do I need an extra VSIshare?
Why do people perform load tests of their virtualized desktop environment? Most likely to get more insight in the performance and maximum capacity of their environment. In order for Login VSI to give you these test results we need data--lots of data. That’s why during a large-scale Login VSI test, logfiles are continuously sent to the VSIshare and sessions are also doing read actions on the files that are located in the VSIshare. This means that a lot of data is written to the VSIshare and sometimes your VSIshare can get overloaded. This can have a negative impact on your test because of 1. loss of test data and 2. timeouts during copy actions.
How to see if this happened during a test
The best way to find out if this is happening during your tests is to open the Analyzer and look at the VSImax v4 Scatter tab. The data is by default presented with response times in milliseconds on the Y-axis and the amount of sessions on the X-axis.
To see if the VSIshare is the bottleneck we should sort the scatter chart by time. This can be done in the dropdown menu underneath the chart. Now that we have sorted the chart by time, the Y-axis is still showing the response times in milliseconds but the X-axis will show the time when the data was collected.
The chart should show a steady line of results just like the graph that is sorted by the amount of active sessions. A lot of gaps between the data (like the screenshot below), indicates that the results can’t be written to the VSIshare and your VSIshare was overloaded during the test.
A lot of gaps in the VSImax scatter chart indicates that your VSIshare was overloaded during the test
How to solve the issue
Issues are there to be solved. One way to solve this issue is by decreasing the load on the VSIshare by moving the Data Servers and Webservers to a second VSIshare. First create a new VSIshare on a different server and copy the _VSI_Content and _VSI_Websites folder into the new share. Now that the new share is created we need to go to the Data Servers tab in the Login VSI Management Console and adjust it with a double left click on the UNC Path. Besides the Data Servers we will also need to change the UNC path for Web Servers, this can be done with a double left click on the UNC path at the Web Servers tab in the Management Console.
The Data Servers and Web Servers are now hosted on a different machine. This will reduce the load on the VSIshare and gives you the opportunity to re-run the test without the Login VSI share being overloaded.
Another easy solution is a RAM disk. Often the I/O load on the server where the VSIshare is hosted seems to be the bottleneck. Several tools give you the possibility to create a RAM disk. This will create a disk located on your memory. Move the VSIshare to the RAM disk and your VSIshare will get an IOPS boost.
A large-scale test generates lots of data, this data can cause the VSIshare to become overloaded. A lot of gaps in the VSImax scatter chart can help you to locate this issue. To solve this we can create a second VSIshare for the Data Servers and Web Servers OR create a RAM disk and move the VSIshare to get an IOPS boost.