Yellow Bricks

by Duncan Epping

ft

Mythbusters: Hyperthreading and VMware FT

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When vSphere was still in beta one of the requirements for using FT was to have hyperthreading disabled. For most people this wasn’t an issue as traditional hyperthreading usually did not improve performance and thus was disabled by default. However with the Nehalem all this changed. Of course I can’t guarantee a specific percentage of performance increase but increases of up to 20% have been reported which is the primary reason for having HT enabled on any Nehalem system.

As you can imagine the HT requirement for FT has been floating around ever since and is a myth which have never been debunked. I’ve spoken with product management about it and they confirmed it’s an obsolete requirement. Hyperthreading does not have to be disabled for FT to work. Or to put it even more strongly: FT is supported on systems which have hyperthreading enabled. Product Management promised me that a KB article will be created to debunk this myth or an entry will be added to the FT FAQ KB article soon.

UPDATE: The FT FAQ KB Article has been updated and includes the following statement.

Does Fault Tolerance support Intel Hyper-Threading Technology?
Yes, Fault Tolerance does support Intel Hyper-Technology on systems that have it enabled. Enabling or disabling Hyper-Threading has no impact on Fault Tolerance.

vSphere CPU Scheduler whitepaper, this is it!!

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This is the whitepaper I’ve been waiting for. By now we all know that the CPU Scheduler has changed. The only problem is that there wasn’t any official documentation about what changed and where we would benefit. Well this has changed. VMware just published a new whitepaper titled “The CPU Scheduler in VMware® ESX™ 4“.

The CPU scheduler in VMware ESX 4 is crucial to providing good performance in a consolidated environment. Since most modern processors are equipped with multiple cores per processor, systems with tens of cores running hundreds of virtual machines are common. In such a large system, allocating CPU resource efficiently and fairly is critical. In ESX 4, there are significant changes to the ESX CPU scheduler that improve performance and scalability. This paper describes these changes and their impact. This paper also provides details of the CPU scheduling algorithms in the ESX server.

I can elaborate all I want but I need you guys to read the whitepaper to understand why vSphere is performing a lot better than VI 3.5. (I will give you a hint: “cell”.)

Another whitepaper that’s definitely worth reading is “Virtual Machine Monitor Execution Modes: in VMware vSphere 4.0“.

The monitor is a thin layer that provides virtual x86 hardware to the overlying operating system. This paper contains VMware vSphere 4.0 default monitor modes chosen for many popular guests running modern x86 CPUs. While most workloads perform well under these default settings, a user may derive performance benefits by overriding the defaults. The paper examines situations where manual monitor mode configuration may be practical and provides two ways of changing the default monitor mode of the virtual machine in vSphere.

And while you arealready taking the time off to educate yourself you might also want to read the “FT Architecture and Performance” whitepaper. Definitely worth reading!

ftCLI.pl – VMware Fault Tolerance Management

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William Lam did it again. He created a script that manages FT from the command line. The script is called ftCLI.pl and here are the details:

Description: Managing VMware Fault Tolerance via the command line.

Params: The following operations are supported: create|enable|disable|stop

Requirement:
vSphere vCenter 4.0
ESX(i) 4.0
Advanced, Enterprise, Enterprise Plus or Eval licensing

Assumption: Your environment is FT capable and is configured properly

I think it speaks for itself. If you are a command line guy this is really useful! Great work William, keep it up! Just head over to the VMTN Communities for the download link and more details on how to use it.

Marathon HA/FT vs VMware HA/FT

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A couple of days ago I linked to Mike D. response to Marathon’s blogs. Mike has updated his original blog article and added a second article which responds to another blog by Marathon. Those who are interested in the difference between Marathon’s and VMware’s products should definitely read it. Especially if you’ve only read the Marathon posts so far. Mike D. sets the record straight!

Marathon FT and VMware FT

a short outtake: “This wasn’t talked about but Marathon’s virtualization FT only works with Windows 2003 Standard or Enterprise SP1 today. VMware FT works with any of the over 70 certified guest operating systems that run on Virtual Infrastructure. The Marathon solution also sits deeply embedded within the OS.”

Marathon everRun vs VMware HA – Another Mess

a short outtake: “As you can now see, Marathon obviously has never touched a VMware host to setup VMware HA. They simply type what they want customers to hear on their webpages time and time again and rely on that FUD to get them sales.”