August 15, 2007

Mainframe Linux at SHARE

Author: Nathan Willis

San Diego -- IBM's customer training and support group SHARE is holding a week-long seminar and conference at the Manchester Grand Hyatt here this week. SHARE dates back to 1955, and the folks gathered in San Diego include programmers, sysadmins, and IT directors who have spent decades running mainframe systems for the world's largest companies and governments. Most of the classes and labs focus on "big iron" products like the mainframe operating system MVS and the CICS transaction server, but Linux is getting strong promotion as well. IBM champions Linux for its zSeries mainframes as the industrial-strength virtualization platform, and judging by the turnout at the Linux and VM program sessions, interest is high.

Most SHARE members are regular attendees at these events year after year. Most of the people at the overview session were on a first-name basis with the presenters and each other. If (like myself) you have spent most of your time working with Intel-based PC and server hardware, it may surprise you to learn that there are other fields of computing where you can spend an entire career and never cross paths with the IA-32 instruction set. But that is the mainframe world.

Mainframes have an entirely different architecture, built around different expectations. They are designed to run at close to full capacity around the clock, using dedicated I/O processors that can move data from storage to the application processors and back along multiple, parallel paths. On an Intel-based Web server, one speaker noted, you start to worry if CPU load hits 20 percent regularly, and you buy another server to help share the workload. To the mainframe crowd, that is a waste of both money and hardware; mainframes run happily at 80 to 90 percent load, continuously.

And mainframers never take the system down, because they never have to (the "z" in zSeries originally stood for "zero downtime," although IBM lawyers now make sure their sales staff say "near zero downtime"). zSeries mainframes are the latest machines built on IBM's S/390 architecture. They are capable of running a variety of operating systems, including z/OS, z/VSE (virtual storage extended), and z/TPF (transaction processing facility).

The Linux solution on zSeries hardware is z/VM, a virtual machine hypervisor that runs virtual servers as guest OSes. IBM ported the Linux kernel to the zSeries architecture in 1998; if you download the kernel source, you will find the zSeries-specific code labelled as s390, right alongside amd64, powerpc, and every other architecture. For the guest OS, IBM officially supports two zSeries distributions: Novell's SUSE Linux Enterprise and Red Hat's Red Hat Enterprise Linux.

Introducing zSeries, and introducing Linux

On Monday, Jim Elliott from IBM Canada gave a talk entitled "Linux on System z: A Strategic View" that covered much of this background material and outlined typical Linux on z/VM usage, from the planning stage to implementation. The question for growing datacenters, Elliott said, is whether to "scale out" by adding additional racks of servers, or "scale up" with many images running virtualized on one mainframe.

In addition to mainframes' heritage of security and high availability -- grown out of experience in the banking industry -- Elliott emphasized the cost savings of Linux on z/VM over traditional server farms. Virtualized Linux images on a single mainframe consume far less space, power, and cooling than rack servers, they are easier to manage centrally, and they require fewer software licenses for datacenter apps like Oracle that are typically priced per-processor rather than per-user.

IBM is taking its own advice. On August 1 the company announced its "Big Green" initiative, in which it will replace 3,900 of its own internal AIX servers with fewer than 30 zSeries mainframes running Linux on z/VM. The mainframes are expected to consume 80 percent less electricity and 85 percent less floor space.

Elliott gave another talk Monday introducing the concepts of Linux and open source. Much of this talk would be common knowledge to open source fans, but it was interesting to hear the statistics about IBM's involvement with open source projects. Elliott said that in 1998, there were nine programmers inside the company working full-time on open source code; today there are more than 1,000, contributing to over 150 projects -- and IBM is the largest contributor to Apache and (surprisingly) Java development. The company even has an internal "open source bazaar" site to centralize the development and maintenance of open source projects used within the company, which Elliott described as functioning like an internal

Questions from the audience

The questions asked by audience members after both of Elliott's talks made for an interesting study of mainframe users' perceptions and attitudes about Linux. One person asked how difficult it was to port Linux and other applications to the zSeries architecture. Elliott chuckled at that one, saying no one had asked since IBM completed the port in 1999. Porting the kernel was easy, he said, noting that the bulk of the work was writing drivers for the mainframes' unique disk and memory management hardware, and most of the changes to the kernel were just for architecture-specific error reporting.

Porting applications to zSeries Linux requires only a recompile, he said. Recently, when an unnamed customer expressed trepidation about porting its app to zSeries hardware, Elliott encouraged them try it and offered to help supply them with resources for the transition. Three hours later, they called back to say that they had tried it and were already done.

Another audience member asked about the differences between Novell's and Red Hat's flavors of zSeries Linux. Elliot touched on the different filesystems, security packages, and kernel versions available, and recommended the Linux for Big Iron site at for more detail. A different questioner asked which distro IBM preferred -- to which Elliott replied that it was officially vendor-agnostic. He did note, however, that Novell accounts for approximately 90 percent of the market, and that neither distro provider had a booth on the SHARE expo floor.

After the intro-to-Linux-and-open-source talk, I asked Elliott what the most common questions and misconceptions were that he heard from mainframe customers. The answer is different for Linux and for open source, he said. With open source, the main question is about legality. The frequency of the misconception is decreasing, but there are still managers out there who have heard that using open source code means you have to release your own code publicly. "I'm pretty sure they're hearing that from one particular company up in Redmond, though," he added.

A different concern crops up in regard to Linux itself. Everyone is already using Linux somewhere, Elliott said, but there are still people who are afraid to put their mission-critical applications on it for fear that it is not robust enough. To answer that criticism, he has a portfolio of IBM zSeries customers. The executive level isn't the problem, he observes, and all of the young people coming out of college already know and use Linux. But there are still pockets of middle managers who have yet to run across Linux firsthand in their own departments. Given the length of time that mainframe users commit to their platform once they implement a solution, though, the safe bet is that once Linux on zSeries hardware is installed, it is there to stay.


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