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Using the LPAR or VM guest options provide great flexibility in how you structure your Domino for Linux on zSeries system. There are advantages to running either configuration, and there is no single best approach. To help you determine the right configuration for you, we now discuss how the configuration decision affects Domino.
You can run several Domino servers in a single Linux for zSeries LPAR. These can be partitioned servers or (with Domino 6) independent servers. Partitioned servers share the same executable Domino code. Independent servers have separate program directories and executables. Domino 6 introduced the ability to run more than one independent Domino server in an LPAR. This provides you the flexibility to manage the servers independently, even though they are running in the same LPAR.
When running multiple partitioned servers in an LPAR software, upgrades are simpler. You can upgrade all servers at one time. You can assign several CPUs to an LPAR, thus allowing you to scale to larger Domino servers.
The Linux that supports Domino on zSeries is a 31-bit implementation, so the LPAR is effectively limited to 2 GB of memory. Although you can use XPRAM for paging to expanded memory, it is not clear that this significantly improves the scalability of Domino.
If you run independent servers, they must be upgraded individually. Although offering more flexibility, this adds to the administrative workload.
With z/VM, you can run multiple Linux guests in a single z/VM LPAR. This gives you more options. You can run each Domino server in its own Linux guest. You can also run multiple Domino servers in a single Linux guest, just as you can run multiple Domino servers in an LPAR without VM.
If each Domino server is in a separate VM guest, you have better server isolation. You can easily separate servers for development and testing from your production servers. You can also separate application servers from mail servers. It is an ideal environment for an application service provider (ASP) who wishes to run many small Domino servers for separate customers. z/VM lets you set the execution priority of individual guests so you can, for example, provide a higher level of service to a production mail server and lower priority to an application development server.
With z/VM, you can utilize the memory above 2 GB (which Linux in 31-bit mode and Domino cannot)., which can be useful if you are running a number of Linux guests. You also gain a single point for administering all of your Linux installations. z/VM does a good accounting job for resources used (unlike a Linux LPAR) and allows you to charge Linux systems accurately. z/VM is written to maximize utilization of zSeries resources.
There is some overhead in having z/VM. You would probably not select this method if you are planning to stay with one or two Domino servers, unless you require the isolation and flexibility that VM provides. However, VM does manage and utilize zSeries resources better than native Linux.
Ultimately, the best way to run Domino for Linux on zSeries depends upon your implementation. If you are planning just a few Domino servers and do not already have z/VM, you may have no reason to bring it in; Linux will run Domino servers in a native zSeries LPAR. You should monitor utilization of resources such as memory to ensure that Linux is maximizing the zSeries potential.
On the other hand, if you are planning to have more than a few Domino servers, even if some of the servers are small, then we recommend that you implement them under VM.
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