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Linux on the mainframe -- is it right for you?

Running Linux on a mainframe isn't the right move for everyone, but an increasing number of customers are choosing this route.

Pioneers like Merrill Lynch & Company Inc., General Electric Co., Grede Foundries Inc. and Sabre Inc. have publicly disclosed that they're using Linux on mainframes. Most companies following this trend are trying to take advantage of mainframes that aren't being used to their full capacity, consolidating scores -- if not hundreds -- of applications that had been running on separate front-end servers.

At this point, more than 300 mainframes are running Linux production systems, with another 800 or so systems still in testing mode, according to Pete McCaffrey, IBM's zSeries product marketing manager. The company estimates that customers must consolidate at least 30 front-end servers for the move to be cost-effective, he said.

Making a business case for running Linux on an existing mainframe is easy, most experts agree, if there are enough front-end servers to consolidate, and if the application base on those servers is primarily Linux or Unix. But if it's mostly Windows servers you want to consolidate, it gets more expensive, because then you need to factor in the costs of software conversion and, in some cases, entirely new software, plus training, support, and so on.

Still, given the right conditions, running Linux on an existing mainframe "almost becomes free at a certain point," said Bill Claybrook, a research director at the Aberdeen Group, a Boston-based consultancy. Yes, there are some upfront costs for a mainframe-based Linux operating system and its accompanying software, but making the move can ultimately lower other mainframe software costs.

IBM offers a deal to its mainframe customers running Linux. If the customer choosing a number of processors on which to run Linux -- say, three processors in an eight-processor system -- IBM lets the customer pay less for other software. For the five other processors, the user pays for "regular-issue" mainframe software from IBM and other vendors. Because Linux software is less expensive than the traditional types of big iron software, this can wind up being a good buy for the customer.

There's also another type of mainframe Linux customer: one who's bought a mainframe specifically to run Linux applications. In the past year or so, McCaffrey said, IBM has sold about 100 mainframes to customers who had never before owned any big iron, and almost all of the machines were bought to run Linux.

All told, about one-fifth of IBM's mainframe business comes from Linux, McCaffrey said.

If you're new to the mainframe world, however, it's key to have knowledgeable and experienced staff before making the move, advised Russell Pavlicek, a Linux consultant and author based in Mount Airy, Md. "The mainframe mindset is very different from the rest of the IT world, because you're dealing with huge things," he said.

Still, it can be worth the move. When properly maintained, mainframes are famously reliable. "You don't worry about downtime or missed transactions, or much of anything else," Pavlicek said.

The biggest Linux-migration issue is often software; many applications aren't available for Linux. While it's true that many of the leading enterprise vendors -- including Oracle Corp., SAP AG, and PeopleSoft Inc. -- have embraced Linux, much of the vertical software for banking, and other specific applications, may not be there yet.

And even if your major applications can be easily ported, don't discount things like device drivers and other relatively minor issues. They may be inexpensive in terms of capital outlay, but they still require time to resolve.

Most observers agree, however, that regardless of whether a user has to acquire a new mainframe, the Linux-mainframe combination represents an infrastructure that's much easier to manage, because it's consolidated. "The question is whether it can save money, improve response time [and] if it's less expensive to administer" than the current setup, Claybrook said. "Linux on a mainframe is a great deal, for some people."

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