Originally Published: Monday, 12 February 2001 Author: Matt Michie
Published to: featured_articles/Featured Articles Page: 1/1 - [Printable]

Linux Kernel 2.4 Ascends The Big Iron

Find out how the new Linux kernel 2.4 increasingly supports higher-end machines, such as the IBM S/390 Mainframe, and Beowulf clusters in this latest kernel month article.

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The new Linux kernel 2.4 increasingly supports higher-end machines, such as the IBM S/390 Mainframe, and clusters. 2.4 also better supports many of the peripherals associated with this class of machine, like gigabit Ethernet, fast-switching, multi-device support for RAID and LVM, improved SCSI drivers, and more.

IBM, as part of its pledge to greater serve Linux with support, software, and services has several mainframe class machines available from the factory with Linux installed. The IBM S/390 has received the most attention from the Linux community, after it was announced that David Boyes at Dimension Enterprises had run 41,400 separate instances of Linux simultaneously on one mainframe machine before it ran out of resources.

David Boyes said, "The test succeeded in demonstrating the capacity of Linux for S/390 for a telco that was considering the purchase of 25 Sun servers to provide ISP and ASP services. Dimension worked with the telco to consolidate its distributed Internet news service onto the S/390. The initial phase included 250 production Linux servers running on a single S/390. Later, it was expanded to 650 production Linux servers on a single S/390 server."

---Linux for S/390: A report from users

The S/390 has an interesting feature where a guest operating system can be loaded into a Virtual Machine (VM). So what good is this? Picture the needs of a web hosting company, their higher end customers demand a dedicated machine running Linux. This way, the customer has full root access, and can install and remove software as they see fit. They need not worry about other customers messing with thier configurations.

This is ideal for the customer, but can create problems for the web hosting company. As their customer base grows, they will run out of space in their colocation facility. Even with rack-sized systems, it won't take long before there isn't enough room for more dedicated customers.

Instead, if this same web hosting company were to buy a mainframe about the size of a refrigerator, they could partition the machine into several thousand separate Linux instances. Each instance is dedicated to one customer, who would have root access to that instance. Because of the partitioning between instances, all of the virtual machines can't interfere with each another.

It is also an advantage for the web hosting company, because dedicated mainframe hardware has always been designed with high availability and reliability in mind. Often, they are many times more stable than commodity PC hardware. The price ratio is also favorable even with commodity hardware, several thousand dedicated boxes add up quickly.

Mainframes, often thought to be dinosaurs by newer generations, seem to be making a Jurassic Park comeback. Once highly proprietary, mainframes are now adopting open standards like TCP/IP, gigabit Ethernet and Linux.

In kernel 2.4.1 the /usr/src/linux/arch/s390 directory contains the following s390 architecture specific files:

36k s390/boot
428k s390/kernel
28k s390/lib
36k s390/mm
28k s390/tools/dasdfmt
40k s390/tools/silo
72k s390/tools
620k s390
620k total

With only half a meg worth of code, the kernel can support this mainframe. It is amazing that the majority of the same code which runs on a mainframe also executes on your home PC. This unified code base benefits both mainframe and home users.

Another important big iron feature with 2.4 support is clustering. In the Linux world, most users quickly hear of the fabled Beowulf. No, not the epic poem, but an open source clustering software solution, originally developed by NASA's Goddard Space Flight Center.

From the history of Beowulf: "In the summer of 1994 Thomas Sterling and Don Becker, working at CESDIS under the sponsorship of the ESS project, built a cluster computer consisting of 16 DX4 processors connected by channel bonded Ethernet. They called their machine Beowulf. The machine was an instant success and their idea of providing COTS (Commodity off the shelf) base systems to satisfy specific computational requirements quickly spread through NASA and into the academic and research communities."

As commodity Intel hardware become both faster, and cheaper, it was almost natural to connect together off the shelf PC's into clusters. Linux, being open source and easily modified was also ideal for this purpose. In fact, some of the faster super-computers in the world run Linux Beowulf clusters.

One thing Beowulf needs more than anything else is fast interconnections. Unless a parallel program is "embarrassingly parallel", each of the nodes has to talk to one another to transmit and receive data. With a slow network, fast CPUs end up stalling while communication is taking place, slowing down overall computation. Kernel 2.4 continues to and improves its support devices like gigabit Ethernet, and other advanced networking solutions to help alliviate communications problems.

2.4 continues to builds on Linux's excellent 64-bit support, in the process making Linux the first out the door with IA64 (Itanium) support. Linux also has excellent Alpha support, which many Beowulf clusters have used to great effect. Portions of Titanic were rendered using a Linux Alpha Beowulf cluster. Many scientific labs also use Alpha Cluster for complex models, like weather simulations.

With growing support for mainframes, Linux will continue to find its way into new and interesting niches. Someone trained in Linux in college, may very well find themselves with a job working with mainframes, with very little re-training required. Linux is quickly become the UNIX, running on everything from a hand-held device all the way to a mainframe. Tune in next week to find out how the same 2.4 kernel runs on embedded devices and PDAs.

Resources:
IBM Mainframe Home
IBM Linux Home
Linux for the S/390
Beowulf Home
Beowulf at NASA/GSFC
Beowulf Underground

Matt Michie exists in the New Mexican desert. Please visit his web site at http://daimyo.org.





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