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The articles touting Linux on the mainframe seem to be getting more frequent. Unfortunately, they also seem to be getting even more enthusiastic. The latest example, TCO: Linux Delivers On Big Iron, published at Computerworld, makes a number of questionable comparisons, nicely summarized in a table at the end of the article. Let's look at some of the problems:- A single-cpu mainframe is compared to a multiple-cpu Intel server. While they list a huge price penalty for the mainframe of 5 to 80 times the cost of the Intel box, they then conclude that the consolidation of hundreds or thousands of Intel boxes onto a single mainframe makes economic sense.
Perhaps that would be true, if the only two options were a mainframe and a huge number of Intel boxes. Even then, it only makes sense if each Intel server is greatly under-utilized. If the Intel servers are actually consuming a significant fraction of their computing resources, the mainframe quickly becomes a very expensive alternative. Consider one hundred uniprocessor Intel systems using, on average, 20% of their cpu resources. Assuming those boxes are fairly modern, that would require roughly 20 mainframe CPU's to handle just the average workload. Usage peaks might raise the requirement to 25 or 30 mainframe processors. The $250,000 to $400,000 single-cpu mainframes cited are, of course, not an option. And, of course, if the individual applications don't actually require separate instances of an operating system, then a single large Intel system, or even a comparable Linux-capable Sun system, becomes a much cheaper alternative. Computing workloads that both require hundreds of separate instances of an operating system and require very little computing power for each one are very few. - The article makes the point that individual seat licenses for Netware, Microsoft Windows, and Unix raise the cost quickly for the Intel solution. This point is simply irrelevant. If Linux can be used for the applications on the mainframe, Linux can also be used on the Intel box, resulting in zero additional costs for the Intel solution.
Similarly, the point is made that up to 41,000 instances of Linux can be run on a single mainframe with a single license. Of course, 41,000 instances of Linux can run on other systems with a single license and for zero cost. Meanwhile, the article quotes a $200,000 charge for the licenses required to equip a mainframe to run Linux. It appears that this mainframe advantage becomes a very large disadvantage when the bills come due. - Another point is that a mainframe takes less floor space and uses less electricity than a "large network of servers". Of course, a large Intel SMP server or a large Sun system is also smaller and uses less power than a large network of servers. And, if separate systems are really needed for the Intel solution, maybe a dense blade configuration would have been an appropriate comparison.
What I would like to see is an in-depth article comparing Linux on the mainframe against appropriate alternatives, not system configurations that would themselves lose in comparisons to various other solutions that were not included in the article.[Related story: The Warmblooded Dinosaur: Linux on the Mainframe]
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