Understanding Performance of NetScaler VPX

An article by Kirk Manzer from Citrix Blogs

In the Solutions Lab, we utilize NetScaler technology in all of our projects for a simple reason. It is often much easier to deploy VPX instances or leverage SDX systems running VPX instances rather than track down actual appliances. VPX instances allows us to be much more flexible in the lab environment. So, understanding how a VPX performs in supporting XenDesktop ICA users has become important

How We Recently Tracked NetScaler’s Performance

As a start, we deployed a default VPX configuration with 2 vCPUs and 2 GB of memory running release 10.5 with virtualization optimized and 8 Gb license. To track the performance, HDX Insight was used to monitor the VPX. The focus in HDX Insight was:

  1. Packet CPU Utilization
  2. InUse Memory
  3. ICA RTT times.

Guidance from the NetScaler experts told us that the ICA RTT times should be below 250ms for optimal performance. Packet CPU Utilization should be around 80%. A single VPX was used for testing, so no load balancing. Finally, SSL was used only for use ICA connections.

To Put the VPX Under Load

We started a 1000 user test. At 500 users the system was at Packet CPU Utilization of 60% and RTT was at 11 ms, well within desired ranges. However, at 1000 users utilization was at 100% and RTT times were at 1.3 seconds.

A second run was done taking more snapshots. Again at 500 users the utilization was at 60% and RTT times were 13ms. As we past 750 users, things got interesting. At 761 users utilization was close to 100%, but RTT time was at 95ms. At 779 users the RTT time jumped to 260ms.



So at 750 users, we were over 90%. Packet CPU utilization and RTT times were still in the double digits, but it quickly rose to unacceptable as we moved past 750 users. From this, a default VPX with 2 vCPU and 2 GB of memory is best utilized at 500-750 users. We did in one test push the VPX to 1300 users, no users were dropped but the RTT time got over 2 seconds. Response was slow, but it was still connected. In all of our tests the InUse Memory never exceeded 60% even under the heaviest load. The default VPX uses a 2K cert, we did test one run with a 4K cert and that increased InUse memory by about 10%, but had no other affect on performance.

We Now Had an Understanding of the Default VPX.

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