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The conclusions drawn from the performance experiments were very positive. Expected storage constraints did not materialize under the loads applied, and with the exception of a default arbitrary limitation of open files, performance was as good as, or better than, early projections. The loads utilized for our experiments did not push storage or I/O limits, so there is more to learn in these areas. But this book will provide a foundation for productive use from Domino on Linux running under z/VM.
These results under VM may not be the same as running Linux in native mode.
However, we did find high CPU usage during a number of our tests. While a zSeries system can run well at 100%, this situation should be monitored in a production environment and tuning steps should be taken to reduce CPU utilization where required.
In our situation, we had only two CPUs dedicated to our testing, and we also used virtual disk for swapping. These two factors could be looked at in more detail to reduce CPU utilization. Be sure to examine both the Linux measurements and the VM CPU usage for a total picture.
In summary, this tuning is not as simple as applying tuning experiences from other platforms. You must know the resources available on your VM machine or native system, and then perform some measurements with your specific workload and environment.
A positive experience in our analysis was that, as potential bottlenecks were found, technology could be applied to alleviate them. Will it be possible to run hundreds of Linux servers each running Domino? That will depend on storage requirements and the types of users—but the underlying technology is sound.
One of the more useful lessons learned during this project was the value of using virtual disk to alleviate Linux storage contention. When using virtual disk for swap under z/VM, it became a dynamic pool of storage for Linux to utilize when needed. However, higher CPU utilization is a normal trade-off for the convenience of using virtual disk. For details on the pros and cons of using virtual disk in storage, see 11.9.4, "Virtual storage vs. virtual disk swapping trade-off" on page 282.
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