Introduction to the z/VM virtualization performance tests
With new virtualization techniques for various platforms in the market, we wanted to test WebSphere Application Server under the virtualization product z/VM. We created and ran performance tests on a customer-like IBM System z environment.
Objectives
There are new virtualization techniques in the market for various platforms. Our objective in these tests was to show the scalability of WebSphere® Application Server environments using the Trade benchmark running under the virtualization product z/VM®. One environment consisted of an IBM® HTTP Server, a WebSphere Application Server, and an IBM DB2 Universal Database (UDB) all installed on separate Linux® guests. This setup is referred to a triplet in this document.
A special feature of a virtualized environment is that it is possible to assign the guests more virtual resources (memory, processors) than physically available, this is called overcommitment. The possibility to overcommit makes virtualization very attractive because it allows a much better utilization of the hardware resources.
- The effects on the total throughput and CPU load when the number of triplets is scaled
- The effects of overcommitting resources (processors, memory)
- A comparison of the performance (based on the Trade 6 workload) between using Secure Sockets Layer (SSL) encryption and no encryption in our configuration.
- The effects of the z/VM quick dispatch option on our environment
This information will help differentiate the value of an IBM System z® solution against likely competitors.
Executive summary
After running the z/VM virtualization performance tests on our test environment, we compiled a summary of our results and recommendations.
Our test results and recommendations are specific to our environment. Parameters useful in our environment might be useful in other environments, but are dependent on application usage and system configuration. You will need to determine what works best for your environment. For our detailed test results information, see Results for the z/VM virtualization tests.
- z/VM manages resources very efficiently so throughput did not degrade in the overcommitted scenarios. We overcommitted the CPUs up to 150% and the memory up to 25%. On z/VM, the CPU overcommitment had only a slight impact as long as the system CPUs were not fully utilized.
- z/VM optimizations regarding memory handling were very efficient for our scenarios. When comparing the defined virtual machine size with the physical memory we had a memory overcommitment of 25%. However, only about 10 GB of the 25 GB of memory allocated was used. Surprisingly we did not have a memory shortage.
- Using the quick dispatch (QUICKDSP) option for z/VM guests can have a benefit when there are resource (CPU, memory) overcommitments.
- Because response times on z/VM are very short even though the system is already overloaded, it is safe to assume that z/VM would support several more triplets until very bad response times of about half a second or more are reached. When making comparisons, it is important to not only compare the number of supported users or workload, but also the response times the users see.
- Be aware that the hardware platform also contributed to our results. This means that z/VM takes advantage of the System z hardware, which is designed to support virtualization products, using hardware in a shared mode, and is stable with short response times under a heavy load.