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Mainframe Linux vs. Unix

Discover how Linux on the mainframe -- in this case, the IBM System z Server -- compares with Unix, in terms of its availability, features and performance.

Today's new breed of smaller, cheaper mainframes, paired with the Linux operating system, look like an attractive...

alternative to Unix on RISC or SPARC servers. Linux on the mainframe seems to give us the best of all worlds: the dependability and resilience of over 40 years of hardware innovation and a flexible, reliable open source operating system. The big question: When should companies choose Linux mainframes over Unix?

More about Linux and the mainframe:
Linux grid takes out firm's aging mainframe 

Linux on mainframe fits for German SAP deployment

This article compares the features and performance of Linux on the mainframe -- in this case, the IBM System z Server -- and compares it with Unix, in terms of its availability, features and performance.

From a performance standpoint, the mainframe has a number of characteristics that are not as prevalent for its mid-range (Unix) brethren. They include:

  • Dependable single-thread performance. This is essential for optimum performance and operations against a database.
  • Maximum I/O connectivity. Mainframes excel at providing for huge disk farms.
  • Maximum I/O bandwidth. Essentially, connections between drives and processors have few choke-points.
  • Reliability. Mainframes allow for "graceful degradation" and service while the system is actually running.

Price cuts and the 2006 introduction of new System z lines, including the smaller, cheaper mainframes, the System z9 BC, paid off for IBM. IDC'S statistics for 2006 show that shipments of System z mainframe line were up 25%, compared to increases of 10% and 16% for IBM's Unix system p platform and MIPS, respectively.

From a business perspective, the values that the mainframe gives to IBM customers include:

  • Economics -- Prices are flat, and there has been an increase in computation power. Recent averages have shown an increase in performance of 28% per year.
  • Utilization -- Mainframes typically run at 80-100% utilization, while distributed systemS typically run at less then 20%
  • Energy efficiency -- The fact that the mainframe has consolidated processors makes for a more efficient space configuration in the data center. This includes decreased power demands
  • Security -- The mainframe provides integrated security solutions for identity management, encryption capabilities and simplified key management.

We've discussed some of the benefits of the mainframe, but why Linux?


  • Standardization

    Many companies are already running Linux on distributed platforms. For those that already do, in addition to having IBM mainframes running centralized applications, using Linux on the mainframe becomes a natural evolutionary step for their business' mission-critical applications. Virtually any application that runs Linux on Wintel computers will run on System z, with only a simple recompile. This solution provides the organization with a corporate-wide Linux adoption policy.


  • Consolidation

    Many distributed Unix and/or Linux servers can be consolidated onto one System z machine, which leads to substantial cost savings. For example, if a company has a server farm of 200 distributed servers, it can be easily be consolidated into either one or two System boxes, hosting 60-70 Linux servers in a high-availability environment that can scale.

    Installing Linux on the mainframe

    First, you'll have to choose your distribution. IBM supports Red Hat, SUSE and many other distributions without problem. They won't recommend one or the other. I suggest that corporate customers looking to implement Linux should use either Red Hat or SUSE, because of their wide-spread adoption and industry support.

    After you've made that decision, you'll have to go through the following steps:

    • Configure the host environment. Here, you'll need to make the choice whether it will run in virtual machine (VM) mode or LPAR mode. VM mode allows for thousands of Linux guests per IFL and will probably be the best fit for most installations. The Linux partition will also need network connectivity through TCP/IP for telnet access to Linux.
    • After you've received the CD from the Linux distribution you chose, you must make the CD image files accessible to the new Linux partition via NFS or FTP.
    • IPL (reboot, in distributed systems jargon) from the initial ramdisk image
    • Provide the information needed to configure the partition (through scripts or interactively through SSH/telnet)

    What about z/OS Unix System Services (USS), which has been available and tightly integrated into the operating system? Won't you get the best of both worlds: Unix and z/OS? The answer is yes. USS is a certified Unix implementation (XPG4 Unix 95) optimized for mainframe architecture.

    Even the most stringent Unix supporters will back down from this argument, given IBM's push for Linux on the mainframe. Unix has taken a backseat to Linux in recent years, while all new innovation is going on in the Linux arena. The Unix implementation is not native, runs in EBCDIC mode and is just not the most popular of systems in IBM land.

    Other arguments regarding Unix vs. Linux include those discussed typically with respect to any Unix vs. Linux comparison. They include:


  • Support -- If you are already using Linux, why would you want to migrate to Unix? It is more expensive to staff Unix engineers and administrators than their Linux or mainframe counterparts.


  • Flexibility -- Linux, being open source, lends itself to faster innovation, as well as more timely releases of bug fixes. The open source community delivers faster because it does not have to go through the endless development cycles of commercial-based operating systems.


  • Market share -- Unix is undeniably losing market share, while Linux is gaining daily.


  • Open systems -- Where Unix had been known as an "open system" up until the advent of Linux, it is seen more as proprietary today. Anyone that has worked on AIX, Solaris and HP-UX, will tell you that Unix is certainly not Unix. On the other hand, the Linux distributions may have some differences, but the underlying kernel is the same.


  • Price -- Though there is plenty of open source software that runs on Unix, open source and Linux go together like peanut butter and jelly. While not all open source software is free, one is certainly free to modify its source code.


  • Security -- Over the years, Linux incorporated many of the same characteristics and functions found in Unix, including the segmentation of the user domain in a multi-user environment, the isolation of tasks in a multi-tasking environment, a password system that can be encrypted and/or located remotely and much more. At the same time, as an open source operating system, it is supported by tens of thousands of developers worldwide. To reiterate, this allows for better innovation and quicker-to-market features then anything Unix can provide.

    Most of the cons of moving to Linux are eliminated by running Linux on System z. For example, you cannot say that Linux will not scale as much as Unix on System z. You cannot make the argument that there is lack of hardware integration and support, as IBM provides that on the mainframe, unlike running Linux on Wintel. You cannot even make the case that Linux is not enterprise-ready for mission-critical applications, since some of the world's largest banks are running applications like SAP on the IBM mainframe.

    In conclusion, rather than Linux on the mainframe being some kind of oxymoron, it may actually be the best of all worlds. How can you beat the innovate and flexibility of Linux, along with the availability and support of an IBM mainframe?

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