IT Management

As anyone who has read a trade magazine in the last year knows, Linux is making inroads in the enterprise on multiple platforms, especially on IBM zSeries hardware. This article explores assorted positives and perils of Linux on zSeries, from both a business and technical perspective.

WHY LINUX ON zSERIES?

The combination of horizontal and vertical scalability, hardware reliability, and I/O bandwidth offered by the mainframe improves Linux’s already significant appeal, particularly for installations with zSeries systems installed or that have used mainframes in the past.

However, unlike an Intelbased install, which entails taking an unused machine, downloading a free copy of Linux, and installing it, mainframe Linux typically requires more planning and discussion. This is not due to weakness or deficiency in mainframe Linux; rather, it reflects the critical nature and rigid change-control policies typically in force in mainframe installations. These policies comprise a set of checks and balances that operate similarly in concept to those in most systems of government: While they make some things more difficult, through the same mechanisms, they ensure greater reliability and integrity of the process.

It is also true that there are relatively few public success examples of Linux on zSeries. IBM literature talks about Winnebago, Boscov’s Department Stores, Korean Air, and a handful of others. But unless you happen to build recreational vehicles, run a department store chain, or offer commercial air travel, it is easy to dismiss these as not being relevant to your business. Other success stories exist, but are “cloaked” under nondisclosure: These businesses recognize that their exploitation of Linux constitutes a competitive advantage at this stage of Linux market penetration, which they want to preserve.

SCALABILITY

While the proven hardware reliability of IBM mainframe hardware and I/O bandwidth (z990 machines offer up to 512 channels, each with up to 256 devices) add value, the ability to scale both horizontally and vertically is the biggest benefit Linux on zSeries offers over Linux on other platforms.

The modern data center has evolved from the centralized “glass house” with a small number of mainframes to racks of so-called “small” or “distributed” servers, often numbering in the hundreds. This offers numerous advantages and disadvantages (see Figure 1).

Modern, well-managed data centers have noticed that these “inexpensive” machines are not that inexpensive after all. But the past is gone: Other factors, particularly growth of connectivity enabling inexpensive, reliable data sharing across long distances, mean that the traditional centralized, tightly controlled, isolated data center is usually not a realistic alternative.

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