IBM Previews Future z/OS, z/VM Mainframe Operating Systems

Published: February 13, 2007

by Timothy Prickett Morgan

A very large portion of IBM's sales and an even larger share of its profits still come from the mainframe base, and the company can't just sit around collecting cash. Mainframe shops are among the most demanding server users in the world--which is understandable given the high cost of these machines--and Big Blue has to update the software from time to time to give it new functionality. This week, IBM is previewing a set of software upgrades for the mainframe that will come out in stages throughout 2007.

IBM is making the announcements at the SHARE mainframe user group meeting, which is happening in Tampa, Florida, this week.

The two biggest announcements concern future releases of two key mainframe operating systems, z/OS V1.9 and z/VM 5.3. The z/OS operating system was previously known as MVS and OS/390 during the previous mainframe generations. Whenever IBM updates z/OS, it is an exercise in alphabet soup reading that would strain the patience of a scribe. The main thing is that IBM is updating z/OS, which is the key platform for supporting transaction processing systems and batch systems on mainframes, based on feedback from customers. And then IBM decides what current iron the software will run on, which will affect the hardware upgrades that customers will have to plan for in the future.

z/OS V1.9 will be delivered in September, and it will run on the current System z9 Business Class (BC) and Enterprise Class (EC) servers, which roughly correspond to midrange and high-end servers in terms of raw performance. The software will also be supported on two prior generations of midrange gear--the zSeries 800 and 890--and on two prior generations of high-end mainframes--the zSeries 900 and 990 boxes. That means any mainframe that dates prior to 2000 cannot run z/OS V1.9.

The big enhancement coming with z/OS V1.9 is that software scalability is going to catch up with hardware scalability. Prior releases of z/OS could only have a logical partition that spans 32 processors (mainframes have a logical machine hypervisor by default, not as an afterthought), even though the largest System z9 EC mainframes have 54 processors. With z/OS 1.9, the operating system will now be able to have a single partition span all the processors in the box, which means that all of the processing capacity of the biggest System z9 machine--as well as its main memory and I/O--can be brought to bear on a single workload, such as supporting a DB2 relational database. That processor count in a single image includes any special zAAP Java co-processors or zIIP DB2 database co-processors.

z/OS V1.9 will also include improvements to the integrated Unix runtime environment inside of mainframes, which is called z/OS Unix System Services, which IBM hopes will make it easier to port Unix applications to run on mainframes. IBM is tweaking the related Unix File System for z/OS to make it more resilient and to hook into Parallel Sysplex clusters better. IBM is also tweaking its WebSphere development tools so an Eclipse-based graphical user interface can be used to debug compiled System z applications; a new XL C/C++ compiler is also coming out with the updated mainframe operating system, which can compile to native z/OS or the Unix services embedded within z/OS. The TCP/IP stack in z/OS V1.9 will now include policy-based routing of network traffic, and the workload manager in the operating system will also now have policies that better manage workload contention when machines are near 100 percent CPU utilization. This would be a very bad condition for most servers, but on a mainframe, CPU saturation is a goal that is often attained.

To help mainframe shops plan their software and hardware upgrades better, IBM said that it would continue its practice of supporting a z/OS release for three years after its general availability. The company also said that it would keep two prior releases under support as each new release comes to market. So, for instance, z/OS V1.9 will still be supported when z/OS V1.11 comes out years hence, and so will z/OS V1.10. IBM stopped selling z/OS V1.7 in October 2006, but customers can still buy support for it. z/OS V1.8 is the current release. z/OS V1.4 and z/OS 1.5--including the trimmed-down, e-business variants for smaller mainframes, z/OSe V1.4 and z/OSe V1.5--will have their support service cut off on March 31.

z/OS V1.6 gets its support cut off on September 30. IBM also said that z/OSe V1.8 would be the last such lower cost z/OS it brings to market, which will only be available through October of this year; the regular V1.8 software will be removed from the IBM mainframe catalog then, too.

z/VM is an operating system in its own right, of course, but early editions of this software were used by mainframe shops much as virtual machine hypervisors are used on X64 and Unix servers today. The VM platform was for a long time the only way to host multiple and incompatible operating systems on a single mainframe. IBM also has an alternative way to slice up mainframes, called logical partitioning, which was often used in conjunction with MVS and its follow-ons and assisted by special hardware features to run better than it might otherwise. Logical partitions were delivered to help customers avoid having to buy VM and to help with mainframe data center consolidations two decades ago. But VM matured into a platform for supporting certain kinds of workloads, such as Linux instances for infrastructure and application serving, because it allows a mainframe to be chopped into very thin but highly utilized slices.

The reason why z/VM is still used is obvious once you review some statistics. According to IBM, using logical partitioning, a top-end System z9 EC mainframe can only support 60 logical partitions and a zSeries 990 can only support 30 partitions. But a z/VM machine running benchmarks in IBM's labs has been testing hosting more than 1,000 real Linux operating system instances. A System z9 BC machine can host about 600 Linux instances, according to IBM. That is a big improvement from the few dozen Linux images that VM could support five years ago.

IBM has contended for years that it costs less money to run a set of Linux instances on a mainframe over a set time period than it does to buy lots of cheap X86 or X64 servers and put Linux on them. With z/VM V5.3, due at the end of June this year, IBM will push the limits of partition scalability out a little further, allowing a single z/VM instance to span 32 processors in a mainframe, up from 24 processors.

With that 33 percent increase, now a larger block of CPU, memory, and I/O capacity can be allocated to a conglomeration of Linux instances. That means a couple of different things. First, each Linux instance can have more capacity allocated to it, should the workloads demand it. (Dynamic resource allocation is done automatically by z/VM, incidentally. This is the only way to keep a system running at close to peak performance, as Linux, Windows, and Unix platforms providers are learning as they retread the ground mainframe shops went over a decade ago when they virtualized.) The increased CPU scalability of z/VM V5.3 also means that customers with modest Linux instances can add more instances to a box. That means more efficient use of the mainframe, fewer z/VM licenses, and fewer outboard X64 servers.

To balance that expanded scalability, IBM is committing with z/VM V5.3 to go beyond the current 128 GB main memory limit of z/VM V5.2. The company is not saying how much more memory it can add into the operating system just yet. The memory management features in z/VM V5.3 will also know how to take advantage of special memory support in the z/VM Control Program--what we would call a hypervisor today--that makes memory paging more efficient on Linux instances running on z9 BC and z9 EC servers.

z/VM V5.3, like prior V5 releases, only runs on 64-bit mainframe iron. That means it is restricted to the current z9 BC and EC boxes, and the prior zSeries z990, z900, z890, and z800 servers.

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