"There are three ways to run Linux on an S/390: native, in a
logical partitioning environment (LPAR) or under VM/ESA. Running
Linux natively means it is the only operating system and the it
controls the whole machine. When run in LPAR, the system resides on
its own separate piece of the physical hardware, so that the
machine can actually run several different operating systems on the
"VM/ESA -- virtual machine/enterprise systems architecture -- is
IBM's operating system that allows you to simulate a complete
computer environment in software. Multiple copies of Linux can run
side-by-side on a mainframe under VM/ESA, each one operating as if
it was on its own box. So far, most Linux mainframe users seem to
favor running it under VM/ESA."
"Just how many virtual copies of Linux can you run on an S/390?
David Boyes, a Virginia-based engineer, has gained some
notoriety in the Linux community for his "Test Plan Charlie" effort
in which he ran 41,400 copies of Linux on the same S/390 CPU. "Each
virtual machine was a complete multi-user network-accessible Linux
system configured for a specific task," he said. "Some
generated web traffic, some handled network connectivity, others
were applications servers, others were shared file servers." The
system ran smoothly, although it did slow as more virtual systems
were added. It did not crash, however, Boyes says, even when VM ran
out of resources to allocate."
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