If you pulled 10 people off the street and asked them to name the operating system with the highest availability,...
they would probably say "Windows" as it's "available" at any Wal-Mart. But when a number of IT professionals within the midrange server, mainframe and storage sectors were asked that same question, not surprisingly, the response was quite different.
What may be surprising to some, however, was that even pros working outside the mainframe sector said OS/390, the operating system for IBM's 390 mainframe, was one of the most reliable. In fact, about 42% of AS/400 professionals polled, for example, cited OS/390 as the most reliable operating system (besides OS/400 of course). Storage professionals, who run the gamut in their operating system usage, cited the OS/390 as a close second to Unix.
Generally, high availability means an operating system has reached the five nines or 99.999% uptime as IBM's S/390 clusters claim. Such a system would have less than 10 minutes of downtime per year. But such availability comes at a cost as a S/390 cluster would cost millions of dollars. On top of that, skilled workers to operate the machines are also expensive and relatively rare especially compared to Unix personnel.
But adding to the operating system's allure, IBM last week formally released zOS, an update to OS/390. The "z" in the name references "zero downtime," which is also part of "zSeries 900," the new IBM mainframe. The operating system features support for 64-bit real storage, improved security and support for Intelligent Resource Director (IRD), a component that manages processing power to applications.
It's probably not surprising that AS/400 users would chose another IBM product, especially in light of the animosity some AS/400 users feel towards Unix. While the majority of respondents chose the OS/390, there was an ardently loyal bunch, 26% in fact, that said no operating system is as reliable as their beloved OS/400. Unix was a distant third with 12% saying it was the most reliable.
Unix is fine for students who want to learn about an operating system since they can go down to the kernel and play around with it. But the tightness of OS/400 offers the stablility and reliability that businesses need, said John Carr, a longtime AS/400 user and educator. "You can't get under the cover and play with it. You can't see the index structures. This makes for a good business machine (since users can't foul it up)."
Mainframers agree with their AS/400 brethren. About a third of S/390 users polled said no operating system comes close to OS/390 in terms of availability. About 22% cited OS/400 and 18% said Linux.
Of the millions of lines of code in OS/390, over 60% is devoted to keeping the operating system stable and available. Some of the higher-end S/390s are designed for up to 35 years between failures.
"The technology for mainframes have been around for over 30 years. Anything that isn't available 24x7 is a toy," said server consolidation consultant David Boyes of Sine Nomine Associates. "Rebooting the system is not an acceptable option."
Yet OS/390's popularity wanes a bit outside of the IBM server family. In a recent poll of storage professionals, 32% cited Unix as their idea of high availability compared to 27% for OS/390. Windows NT was a distant third with 12% of the votes.
Server market growth, at least for last year, seems to coincide with the storage users polled. While the mainframe market declined 18% to $3.9 billion, the Unix market grew 14% to $29 billion according to IDC.
Yet Big Blue has spent a lot of time and money to stem public opinion of the mainframe as "old dinosaurs." Today's mainframe is a mega-server primed for e-business, IBM contends. The effort seems to be paying off as new capacity purchased specifically for e-business uses more than doubled between from 1999 to 2000 according to Rich Lechner, IBM's vice president, e-business, enterprise servers.For more information High availability operating systems: Reality or future objective? search390 Best Web Links on Operating Systems search400 Best Web Links on OS/400 search400 Best Web Links on High Availability