Five or ten years ago, this sort of question would have been unthinkable, but now mainframe users are increasingly facing a choice between whether to use Linux on System z or z/OS to host new mainframe workloads.
These new workloads may be the result of a consolidation project, or simply taking advantage of flexible architectures like SOA to utilize spare mainframe capacity, but the decision is not an obvious one in either case.
On the one hand, long-time mainframe guys will say that z/OS has grown up with the mainframe and therefore must be the best choice. But IBM has done a lot to its version of Linux for the mainframe, and Linux bigots will be quick to point out that the license costs will be cheaper and there are strong advantages in standardizing on a portable and flexible operating system enterprise-wide. Worst of all, given the polarized nature of IT in general, the decision makers find it hard to get unbiased advice on such a divisive question.
In the end, the answer to the question of whether z/OS or Linux on System z is better is not surprising – “it depends”. This subject is discussed in much more detail in a free Lustratus report, “Choosing the right SOA platform on IBM System z”, available from the Lustratus web store. While this paper focuses particularly on developing or moving SOA workloads onto System z, the analysis applies to any new mainframe workload. Summarizing the arguments in the paper, the major differences that affect the decision are that Linux is designed to offer a common environment across many platforms, and is thus less attuned to individual platform capabilities by definition, and that whereas Linux has been designed for the ‘server’ model where it is used to operating one type of workload, z/OS has been built to handle multiple subsystems from the start.
The common environment aspect of Linux offers flexibility, helps to drive license costs down and leverages widely available skills. The multi-system capabilities of z/OS combined with its close linkage to the System z platform offer the greatest exploitation of System z facilities. But as always the devil is in the details.