The Transition To RHEL 8 Begins On Power Systems

June 10, 2019 Timothy Prickett Morgan

If it is not already obvious to you, Red Hat Enterprise Linux is going to be the default and preferred variant of the Linux operating system that will be available on IBM’s Power Systems and System z servers at some point in the not-too-distant future when Big Blue’s $34 billion acquisition of the commercial Linux distributor closes.

As we pointed out last fall when the deal was announced, we don’t know precisely how IBM will rectify some of the overlaps between the two product lines after the deal closes. What will IBM will do with the WebSphere and JBoss Web application servers? That’s the big question. There is also some rationalization that needs to be done for variants of the OpenStack cloud controller and the Kubernetes container orchestration system that are already made by Big Blue and Red Hat. Both companies also have their own developer IDEs and a bunch of parallel file systems and object stores that conflict with each other in varying degrees. But one thing we know for sure is that RHEL is IBM’s Linux operating system. Period. Full stop.

For Power8 and Power9 shops, this is probably going to mean starting out with RHEL 8, which started shipping on May 7 for X86 platforms and which became available on those two Power processors on May 31 as detailed in announcement letter 219-234. Most Power shops that are using RHEL are probably on some variant of RHEL 7, but the RHEL 7.7 update, which came out in beta last week, is going to be the last supported release of RHEL 7, so if you are starting fresh and provided the applications you are using are going to be open source, created new, or bought from a third party that intends to support RHEL 8, it makes no sense to backstep to RHEL 7. If you have to certify any Linux applications anew, you might as well do it on a release that has another decade ahead of it for regular and extended support, as RHEL 8 does.

Besides, RHEL 8 has tunings specifically for Power8 and Power9 iron and also various innovations that make it better than RHEL 7 anyway.

With RHEL 8, IBM says that the transition from big endian to little endian ASCII character formats is complete, and now Power lines up the bits exactly the same way as X86 and Arm servers do. As for the tuning for Power9, the details are a bit thin, but Big Blue says that there are optimizations for running RHEL 8 using SMT-8 mode on the Power9 processor, which means utilizing the full eight threads per core that the architecture supports and which is probably the way that most IBM i shops should be running their databases and applications most of the time.

The RHEL 8 stack has “incremental improvements” in the KVM hypervisor, which is only important for machines that will be running Linux solely. (IBM i and AIX require the predecessor PowerVM hypervisor to run, which also supports big endian and little endian Linuxes from Red Hat, SUSE Linux, and Canonical.) That KVM hypervisor is also being tweaked to support nested virtualization on Power and X86 platforms, which allows for virtual machines to act as hypervisors for yet another layer of virtual machines that are stacked on them. This is useful for running older operating systems within a more secure newer operating system or for testing applications on old releases. Nested virtualization is also used sometimes to support different hypervisors atop the same physical machine. For instance, VMware’s ESXi hypervisor can run Microsoft Hyper-V, Citrix Systems XenServer, and Red Hat KVM within VMs and then they can each in turn run their own VMs. (This is all on X86 architecture.) It may be theoretically possible to use nested virtualization to run the PowerVM hypervisor atop KVM, and thereby allow for IBM i and AIX to run on any Power Systems machine, not just the ones designated officially by IBM. This is the main reason why IBM i shops might care about this feature, which is still in technical preview.

The Red Hat compiler stack and toolchain has also been tuned to take advantage of all of the features in the Power9 processor as well, which is another reason to go with RHEL 8 on Power9 iron. Presumably this software development stack from Red Hat has also been tweaked to take full advantage of Power8 chips, too, which have a much larger installed base at this point than Power9 iron.

The other innovation with RHEL 8 is called Application Streams, and with this, Red Hat has taken the repository for RHEL code and virtualized it so different aspects of the system can be updated independently and at different rates. The core part of the repository, as Red Hat explains, provides the userspace where applications run in main memory (as opposed to the kernel space where the operating system kernel runs); this is called BaseOS and it provides that userspace for applications running on bare metal, a container, or a virtual machine. The Application Stream part of the carved up repository represents the part of the Linux distribution where applications are bundled in and are intended to run in that BaseOS userspace. These repositories can be updated independently and provide a more flexible way to apply patches. You can just do the core operating system, where the security fixes tend to live for the kernel, or the applications if you have them. (There is another repository slice called CodeReady Linux Builder for the application development tools, and there will probably be more in the future.) The idea is to be able to patch the userspace applications faster than the core operating system space, and in this regard this is a bit like the way IBM handles Technology Refreshes for the IBM i platform.

Power Systems customers can get support licenses for RHEL 8 from IBM through SupportLine for Linux on Power Servers – product numbers 5771-LNX, 5773-LNX, or 5775-LNX – or they can buy support directly from Red Hat or from Red Hat through IBM, which acts as a go-between. In the end, there will just be one RHEL support organization, we presume.

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