1.2 Reasons to run Domino for Linux on zSeries

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Here we discuss why you might consider running Lotus Domino on Linux on the zSeries platform. This section is aimed at managers, decision makers, and planners. For more detailed information on the structure of the solution, see 1.4, "Structure of Domino on Linux on zSeries" on page 6.

1.2.1 Domino on Linux

The Linux operating system is becoming very popular for many applications. Some advantages of using Linux for Domino are:

It allows you to change the cost model for delivering the Domino service. While Linux can be downloaded from the Internet for free, it is likely that you will pay for a Linux distribution, and for Linux support and application software. However, it changes the cost model because Linux runs on many platforms in the marketplace, so you can select the platform that best fits your needs in terms of quality of service (such as scalability and availability), cost, and risk.
It provides a great deal of flexibility, since you can move applications to different hardware platforms without changing them.
It is based on UNIX, and therefore has scalability, availability, and security more like UNIX than Windows.

1.2.2 Value of the zSeries platform

Having decided to run Domino on Linux, the IBM zSeries servers have advantages over other server types:

zSeries servers are the most reliable and scalable servers for mission-critical applications in the marketplace.
You can add capacity to the server while the system is running; this is called Capacity Upgrade on Demand. This allows you to start with a small zSeries server and add capacity as the number of users increases.
A single zSeries server can host many Domino servers spread across multiple images of Linux, thus enabling a single server to support tens of thousands of Notes users and applications.
With this scalability, zSeries can provide a lower total cost of ownership. With fewer hardware servers and Domino servers, you benefit from less complexity and a lower cost of administration and management.
zSeries LPAR technology leads the industry. Its ability to share CPUs between LPARs make it possible to reduce cost by delivering unused processing cycles in one LPAR to an LPAR that requires additional processing cycles. zSeries also makes it possible to configure more LPARs than the number of physical CPUs.
Linux on zSeries provides a very scalable Domino solution by using the new sys_epoll system call in United Linux 1.0 to significantly improve Linux scalability.

1.2.3 Value of z/VM

Linux will run directly on zSeries server hardware, either natively on the whole machine, or in a logical partition (or LPAR; refer to "zSeries Logical Partitioning (LPAR)" on page 9 for more information).

Another alternative is to run the z/VM operating system on the server (either the whole server or in an LPAR,) and then run Linux in one or more z/VM virtual machines. The additional benefits of running on z/VM are:

You can run dozens (even hundreds) of Linux servers on a single system under z/VM, far more than the LPAR method would allow. This enables you to rapidly consolidate many Domino servers to zSeries without needing to change your Domino infrastructure
It is very easy to create and delete virtual Linux guest machines, if you have a need to do that on a regular basis. It is also very simple to move them from one VM system to another, if those systems are sharing DASD.
z/VM provides facilities for system management across multiple Linux servers.

1.2.4 Comparison of Domino on zSeries—Linux and z/OS

With Domino 6.5 there are now two ways to run Domino on a zSeries platform: either on the z/OS operating system, or on the Linux operating system (with or without z/VM). It is not the purpose of this book to recommend one or the other, since the preferred option for you will depend on your specific needs and circumstances.

However, it may be helpful to list some of the different characteristics of these two operating systems as far as Domino is concerned. We have listed these under the three headings that we think you should consider—quality of service, cost, and risk.

Quality of service (QoS)

By quality of service, we mean the standard of service that you are able to deliver to the users, including reliability, availability, serviceability (RAS), scalability, security, and manageability. Linux and z/OS differ in these areas:

While both operating systems benefit from the quality of service features of the zSeries hardware, Domino on z/OS exploits more of the hardware features, such as use of the hardware cryptographic facility that improves SSL performance.
z/OS contains many advanced functions for running mission-critical applications. Half of the operating system kernel is there for error recovery, so the z/OS operating system seldom fails. Many administration tasks can be done without taking the operating system down.
z/OS contains many advanced features for automated system management, including advanced workload management with Intelligent Resource Director, Resource Measurement Facility for performance monitoring, and System Management Facility for resource consumption measurement.
z/OS has been developed over many years to run efficiently on a 32-way processor. Linux is not proven to these levels of scalability, which means that for a large system you will need to run more versions of the operating system. z/VM is proven to run efficiently on many processors, so you could run a single version of z/VM with multiple versions of Linux in separate virtual machines.
Domino on z/OS is proven to run thousands of Domino users in a single DPAR under z/OS. At the time of writing, Linux is not proven to the same levels of scalability.
DECS for Linux on zSeries (Linux or z/OS) currently supports only connections to DB2.

Cost

A second consideration is cost. This redbook cannot provide detailed cost comparisons, but we suggest you keep in mind the following points:

Hardware costs depend on detailed sizing information that is not available at the time of writing. IBM offers IFLs for Linux, in addition to standard zSeries processors. Disk costs are likely to be the same in both options. Keep in mind that hardware costs are likely to be less than one-third of the total cost of running the solution over five years.
Software costs may not differ between z/OS and Linux as much as you would expect. Domino is chargeable in both environments. While the z/OS cost is likely to be higher than Linux, options such as z/OSe on z800 servers (for small to medium installations) can reduce that cost. You will pay for a Linux distribution, and will also probably pay for Linux support. In both cases you will need some additional software, such as for backup.

z/OS costs can limited by using NALC or Workload License Charge, or by running Domino on a separate zSeries server from other zSeries workloads to avoid having to license unnecessary products on Domino capacity. On Linux, other software costs can be minimized by using IFLs, because if you use standard processors, you may again incur additional costs for other products on z/OS on the same machine.
People and support costs are likely to be the highest cost that you incur in running the Domino service. The additional hardware and software costs in z/OS provide you with a great deal of extra function that will reduce your support effort and therefore your personnel costs. Refer to "Quality of service (QoS)" on page 4 for a list of these capabilities, and consider how they will reduce support costs.
Also consider the costs of training and building up experience. Using skills that you have today will avoid the costs of developing or bringing in new skills. If you do not have skills today, Linux skills are more readily available in the market than z/OS skills.

Risk

The third factor to consider is risk. A higher risk project is likely to result in a lower quality of service, at least initially, and a higher cost to resolve unforeseen issues. Factors to consider include:

What level of scalability and reliability do you require? For the highest levels, Domino on z/OS has been proven in the marketplace since 1997. Domino on Linux first became available on Intel® servers in 2000, and first became available on zSeries in 2003.
What skills do you have available? z/OS is a more complex operating environment. If you have z/OS skills now, adding Domino to that environment is relatively simple, but if you do not have those skills, developing them will take time. If you have Linux skills, or UNIX skills, then implementing Domino on Linux should be straightforward.
What is your preferred cultural approach to running Domino? If you have, or wish to have, centralized control, then Domino on z/OS will minimize the number of Domino servers you need to run. If you wish to continue with decentralized control, as perhaps on Windows today, then Domino on Linux will allow you to run many small servers efficiently, especially under z/VM.

In short, z/OS offers the ultimate in zSeries reliability and scalability. You can choose to run Domino on either z/OS or on Linux by considering a number of factors, especially what skills you have available.

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