KVM! Do I even need PowerVM Anymore??

July 19th, 2016

Ron Gordon
Director – Power Systems

My teammate, Chris Minnis, wrote a great blog entitled “KVM! Do I Even Need VMware Anymore?” and in reading it, I was inspired to write a corollary.  In Power Systems, there are now two virtualization technologies available in PowerVM and PowerKVM.  Since I believe you are familiar with PowerVM, I will just focus on a couple of the differences for you that are considering PowerKVM.  First, PowerKVM will only virtualize Linux (Big Endian and/or Little Endian) on Power Systems…  no AIX nor IBM i virtual machines running on PowerKVM, and since Windows does not run on Power Systems, for sure no Windows VMs either.  PowerKVM will only function on POWER8 systems, as it runs in Little Endian mode.  This means that PowerKVM can only run on the LC and L models.  If you acquire a Linux-only Power L server, you have a choice to run either PowerVM or PowerKVM as your virtualization engine for Linux virtual machines.  On the LC servers, you can only run PowerKVM.   So, I guess it comes down to the L models where you have a choice of PowerVM or PowerKVM.

Since you are familiar with PowerVM, I will present some differences between PowerVM and PowerKVM to help you decide which you may choose to use.  PowerKVM from IBM is a “modification” of the open source KVM, in that it has to interface to the hypervisor of the Power System.  The Power hypervisor has also been modified to interface to the PowerKVM, and that version is called OPAL (Open Power Abstraction Layer).   On the L models, you can run with either full pHyp or OPAL, as both are distributed with the Power Systems L models.   Okay, so now we have PowerKVM running, but how does it compare to PowerVM?  First, no VIOS, as the Linux kernel in PowerKVM does the IO virtualization; IO virtualization is limited to KVM supported storage devices and to KVM supported network devices.  In PowerKVM, there are no shared processor pools nor shared storage pools.  In PowerKVM, there are no microprocessor allocations, no “entitled/desired/capped/uncapped” and no DLPARs.   PowerVM features, such as AMD and AMS, do not exist in PowerKVM.  LPM does exist, and priorities to VMs can be accomplished via scripting and setting of PowerKVM parameters.  There are other differences, such as PowerKVM cannot be managed by an HMC, and as such, certain performance monitoring tools that run on the HMC will not be available.   I know that sounds like a lot of differences, but since you are running only Linux, this has proven over time to be what is satisfactory to the Linux community.

Now, let’s say you want to run Linux and AIX and/or IBM i on a single virtualized system.  In that case, you can run both the Power Systems Scale-Out servers and the Power Systems Enterprise servers, and you can support that environment with PowerVM.  I would suggest running PowerVM 2.2.3 or higher since that version supports both BE and LE versions of Linux, in conjunction with AIX and IBM i virtual machines.  When running on PowerVM, all PowerVM functions available to AIX and IBM i fully support Linux VMs.

As a closing comment, if you use PowerVC or PowerVC Manager (aka OpenStack), you will be able to support both PowerVM and PowerKVM environments.

Hopefully you now have the information you need to made virtualization technology decisions on Power Systems.   One view I may offer is that if you are running Linux Clusters separate from your AIX or IBM i systems, then I believe you may wish to consider PowerKVM where as if you are running Enterprise Systems or Scale Out Systems with AIX and IBM i, then I think PowerVM is the logical choice.

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