Linux on big iron: Page 2

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This sort of unlimited scalability, either on multiple virtual machines or on one copy of Linux, seems to be one of the things attracting users to Linux on the mainframe. "What if you could have a system that could run the same software as PC Linux, but could scale to almost any size you needed?" asked a systems programmer at a major medical center in the Midwest, who wished not to be identified by name because the Linux mainframe project at his company is in the preliminary stages. "Instead of 10 or 50 or 100 users, what if you could support thousands in the same Linux image?"

Another draw, says the Toronto Transit Commission's Webb, is ease of use. Adding another Linux server to the mainframe under VM/ESA takes about 30 minutes, he says, and circumvents the need to buy new servers, run cables between machines, or even find a place to plug in a power cord, since the server operates in a virtual environment within the mainframe. And, Webb says, "connections between Linux servers inside a mainframe can be very fast, much faster than our existing Ethernet LAN."

For his part, Boyes believes that one of the largest advantages of Linux/390 lies in the underlying reliability and high availability of the S/390 hardware platform. What's more, he points out, "You don't need a multimillion dollar network monitoring and system management solution--VM includes those tools as part of the base OS, and there are dozens of excellent monitoring solutions freely available."

A time and a place for Linux S/390

Computing advances do not come without challenges, however. The lack of software support will be an issue for some time and will depend solely on the skills of the systems programmers, according to Bill Stephens, a VM systems engineer at a large mainframe datacenter in Philadelphia. Drivers will need to be written for several types of devices.

The Linux for S/390 code is available for download at IBM's Linux for S/390 page.

To subscribe to the LINUX-VM e-mail discussion group, send an e-mail to //
As with any new system, Linux on the S/390 will face some of its biggest hurdles in perception. Marist College in Poughkeepsie, N.Y., has been at the forefront of the Linux S/390 efforts and is the first non-IBM site to run Linux S/390 from IBM. The site launched in December 1999. "For historical mainframe shops, they need to understand that Linux is a viable option for them, and for traditional Linux people, that Linux on 390 can bring things to the discussion," says A. Harry Williams, director of technology and systems at the college. He emphasized that Linux on S/390 is the real thing. "It isn't Linux-like or even Linux-lite. It is Linux," he says.

But Linux on a mainframe is not the right tool for every job, says Scott Courtney, a senior technical analyst at a large manufacturing company and author of a series of articles on the Linux S/390. An S/390 running a light load will not run as quickly as a fast PC server under a light load, according to Courtney. The difference between the two systems will not be apparent until the load is much larger.

"The PC will begin to degrade and will typically reach a point where it avalanches down in performance as its load limit is exceeded. The mainframe starts out at a lower performance level, from the standpoint of an individual program task, but degrades much more slowly and much more linearly as the load increases," he says.

"The mainframe isn't necessarily a better tool than a PC server, or cluster of servers. It is a different tool and offers new possibilities to meet a class of application needs that aren't well addressed by the traditional Linux hardware platforms," he adds.

Daisy Whitney is a freelance writer based in Denver. Her work has appeared in the Denver Post, Electronic Media, and other publications. She can be reached at

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