So reliability is increased not by reducing potential PC failures, but by making recovery from a failure much quicker and simpler. Users can afford to purchase more expensive and more reliable server-class PCs with features such as redundant power supplies and hard disks because there are fewer PCs to purchase, further increasing reliability.
"With virtualization, redundant servers connected to redundant storage area networks that host virtual machines can provide hot-swap fail over capability. If the primary host machine fails, the virtual machines are moved to the secondary host machine on the fly, without interruption," observes Chuck Toth, an MSEE and a consultant at systems integrator Maverick Technologies.
Increased reliability is one of the leading benefits of virtualization (others are listed in Table 1). Chief among these benefits is longer lifecycles for applications, a major boon for process industry firms.
A major complaint about using PCs in process control applications. has been the relatively short lifecycles of operating systems as compared to software applications. For example, an HMI application configured to run on a PC could have a lifecycle of decades, whereas the underlying operating system lifecycle would typically top out at about five years. So a PC failure 10 years into the life of an HMI application would require a new PC with a new operating system, and often major changes to the HMI application. But with a virtualized environment, the lifecycle of the machine no longer depends on the hardware and the operating system, but instead depends on the lifecycle of the hypervisor, which is typically much longer than that of an operating system.
The hypervisor is the software that runs between the PC and the operating systems on a virtualized PC, and it abstracts the PC hardware from the operating system and the application. This is what allows operating systems and associated applications to be moved so easily among PCs in a virtualized environment, whatever the vintage of the PCs.
"With the relatively quick lifecycles of PCs and operating systems compared to the long lifecycles of industrial automation installations, the hardware independence offered by virtualization is very attractive," says Paul Darnbrough PE, the engineering manager at KDC Systems.
In the pharmaceutical industry, replacement of a PC is an event that requires revalidation, upping the cost to astronomical levels. Genentech, a biotech company based in South San Francisco, Calif., specializes in using human genetic information to develop and manufacture medicines to treat patients with serious or life-threatening medical conditions.
"Genentech estimated that the costs to upgrade one of its Windows 95 PC-based HMIs to a Windows Server 2003-based system would be approximately $40,000," recounts Anthony Baker, PlantPAx characterization and lab manager at Rockwell Automation. "Final figures topped $100,000 because of costs associated with validating the system for use in a regulated industry," adds Baker.
"Assuming that the operating systems are updated about every five years, costs quickly become a limiting factor in keeping an installed base of PCs up-to-date. Additional factors like computer hardware changes also contribute to the cost of upgrades, as each change incurs engineering expenses and possibly production downtime," notes Baker.
Instead of investing in costly hardware and software upgrades, Genentech implemented virtualization.
According to Dallas West, the cell culture automation group leader at Genentech, one of the most lasting effects of virtualization is that it allows legacy operating systems, such as Windows 95 and Windows NT, to be run successfully on computers manufactured today. This extends HMI product lifecycles from five to seven years to 10 to 15 years and possibly longer.
"Having the ability to extend the useful life of a computer system allows a manufacturer to create a planned, predictable upgrade cycle commensurate with its business objectives," West says.
"No longer is a business forced to upgrade its systems because a software vendor has come out with a new version. Upgrading systems can once again be driven by adding top-line business value, and by choosing to upgrade only when new features become available that will provide an acceptable return on investment." he adds.
Extending the lifecycle of an application cuts costs, and increasing reliability saves money by avoiding downtime. But the most direct cost savings of virtualization are found by simply reducing the number of PCs (Figure 2), while maintaining all of the functionality of a traditional one operating system/PC configuration.