From its inception, "virtual" computing has had two distinct meanings. At the hardware level, virtual memory or virtual disk allows systems to deliver the speed of a faster, higher level of storage and the capacity of a lower level of storage. Above the hardware level, a virtual machine (VM) allows one system to split into multiple "machines," each with its own operating system (OS). Thus, for example, a System z9 can contain a z/OS VM and a Linux VM, each operating as if it was a separate system. When vendors talk about virtualization today, most of the time they are talking about the second definition.
Virtual machines can deliver greater utilization of hardware than, say, x86 servers, and therefore mainframes and high-end Unix servers with greater apparent hardware license costs can still deliver roughly equivalent license costs compared to a server farm running 20 applications. However, the key cost benefit of virtual machines is lower people costs.
In the mainframe's case, the reason for lower (system) administrative costs is the relative simplicity of the mainframe environment:
The core of IBM's mainframe virtualization offering is z/VM -- the virtual machine OS from which other virtualization solutions, such as VMWare (now owned by EMC Corp.), sprang. Z/VM's Virtual Machine Resource Manager provides not only automatic allocation of system resources between virtual machines but also user control over resource limits, prioritization and SLA (service level agreement) support. At present, z/VM can support thousands of z/OS, z/OS.e, TPF and Linux virtual machines -- all operating on the same single mainframe.
This allows intermachine communication at the speed of placing a message in main memory and picking it up from there and also adds security, since such messages never leave the mainframe. In addition, IBM's security suite protects the data within the mainframe and within each virtual machine.
It is also worth noting that IBM mainframes have been offering virtual memory for longer than most if not all other platforms, and IBM also provides a virtual tape library solution.
Virtualization has always been a strength of the mainframe, but with enterprises increasingly facing the costs of x86-based server farms, mainframe virtualization via virtual machines is more attractive than ever. Its benefits include simplification of the enterprise architecture, lower total cost of ownership, greater scalability and robustness, better security, and more flexibility to optimize the overall enterprise architecture. While the mainframe does not yet support Windows VMs, enough Windows and Unix firepower has been added to Linux to make most applications on any platform easy to move into a mainframe Linux VM.
Over the next few years, as IBM and others continue to virtualize their full software architectures so that applications do not care what platforms they run on, a relatively cost-effective, scalable, robust, secure platform is likely to be the platform of choice, no matter what its name or pedigree. The mainframe is presently in a good position to be such a platform.
About the author: Kernochan is president of Infostructure Associates.
This was first published in June 2006