Using Linux as a mainframe OS links flexibility to the power of big iron, and can help large companies significantly reduce data center operating costs and complexity.
The hype around such converged infrastructure systems as Cisco's Unified Computing System has led data center administrators to recall that one type of converged infrastructure system has been around for a long time: the mainframe.
Think of a mainframe, such as IBM System z, as a collection of computers, not just one computer system. Data centers can operate one mainframe much more efficiently than hundreds of physical servers, lowering operating costs. Inside the monolithic physical box of a mainframe are logical partitions (LPARs) that run as independent physical machines with the option for different OSes. These include the Linux operating system, which offers cost savings and flexibility compared to the proprietary and closed-source OSes, such as OS/390.
Running Linux on mainframe hardware
An LPAR is hardware-based virtualization; the hardware in an LPAR can dynamically expand if required. Within the LPARs exists a second level of virtualization, the z/VM hypervisor that understands and accesses the mainframe hardware.
For a third layer of virtualization -- typically only needed for testing -- you can install a z/VM within the z/VM hypervisor.
Linux mainframe OSes run on top of IBM's Integrated Facility for Linux (IFL). This IFL processor only runs Linux, and therefore costs less from the mainframe vendor than general-purpose processors.
Redundant processor execution steps and integrated checks in mainframe hardware guarantee that no data will be lost, even if a processor fails. IBM mainframes also use HiperSockets, fast TCP/IP connections that exist in memory only and are inaccessible to intruders. Finance and other high-reliability sectors place a premium on reliable data processing from mainframes.
Mainframe software development
Companies are using Linux mainframes to perform mission-critical tasks in corporate environments. Plenty of open source Linux distributions are available for the mainframe, but most companies that have invested the money into purchasing a mainframe should also spend on an enterprise Linux distribution. Companies don't want to cut costs for software support and find out at the end that they're on their own when problems arise.
While mainframes offer many benefits, it can be hard to develop Linux software for them. Only large, well-funded companies can afford to buy a mainframe, and it is difficult to develop software for mainframes without one. By contrast, most companies can afford an Intel-based server system for software development. Software developers can use mainframe emulators, such as the free Hercules emulator, to develop Linux-based software that runs on mainframe hardware.
About the author:
Sander van Vugt is an independent trainer and consultant based in the Netherlands. He is an expert in Linux high availability, virtualization and performance. He has authored many books on Linux topics, including Beginning the Linux Command Line, Beginning Ubuntu LTS Server Administration and Pro Ubuntu Server Administration.