Author Archives: Krishna Raj Raja

VMware Fault Tolerance Performance

If you have been following the virtualization blogosphere
then you may have noticed that last week we published three interesting
performance whitepapers at once. I want to talk about the “VMware vSphere 4
Fault Tolerance: Architecture and Performance”
whitepaper in this blog.

VMware Fault
Tolerance also known as FT is one of the most anticipated features of the
vSphere 4.0 release. FT provides continuous high availability to virtual
machines without down time or disruption in the event of complete host failure
and it is designed to be agnostic to the guest operating system and the
application running in it. With FT you could get hardware style fault tolerance
protection to virtual machines on commodity server systems without the need for
any specialized hardware. All you need is recent processors from Intel and AMD
and a gigabit Ethernet Link for transmitting FT logging traffic. You could
download and use the VMware Site Survey
utility
or check KB article
1008027
to see which servers in your datacenter have FT compatible
processors.

We first demonstrated a prototype version of FT at the VMworld 2007
keynote
, and earlier this year at VMworld Europe 2009 we previewed its performance
characteristics.  The product is now officially
shipped with vSphere 4.0 and  some of you
may be already using the feature and many others are probably planning to use
it in their datacenters very soon. In case if you are wondering how enabling FT
impacts performance we got you covered in the whitepaper. This whitepaper
provides concise but important architectural and performance aspects of
enabling FT backed up with performance data from variety of workloads. We have
been working very hard on enhancing the performance of FT for the last few
years and you’ll be able to see the results in the whitepaper.  The two key takeaways that you will learn
from this paper are that you don’t need lot of networking bandwidth for FT; a
gigabit link is sufficient for the vast majority of workloads.  Also when there is sufficient CPU headroom FT
impacts throughput very little.  For more
details I recommend you to take a look at the whitepaper. 

I also welcome you to my VMworld 2009 session in San Francisco
titled “BC2961:
VMware Fault Tolerance Performance and Architecture”
where I will be
talking more in depth with recent performance numbers. 

VMI performance benefits

One of the hallmarks of VMware has been its continuous innovation. With every new release VMware adds exciting new features to its products. But there are also lots of changes in each release that may not be as obvious, but are still quite important. Performance improvements often fall into this category. One such feature that was added in VMware ESX Server 3.5 is the support for guest operating systems that are paravirtualized using the virtual machine interface (VMI) specification.

A little bit of history will provide insight into the motivation for the VMI standard. Previous Linux paravirtualization efforts produced paravirtualized kernels that were tightly coupled to the hypervisor.  Frequent interface changes led to guest kernel and hypervisor version dependencies, impeding the independent evolution of the kernel and the hypervisor. These paravirtualized kernels were also not compatible with native hardware. Wouldn’t it be nice if a single kernel could run both natively and in a virtual machine, but with improved performance using paravirtualization in the latter case? This feature, now called transparent paravirtualization, was non-existent. The lack of transparent paravirtualization doubled the number of kernels to develop, test, and debug. In order to address these issues VMware proposed the VMI paravirtualization standard in 2006. As a proof of concept VMware implemented the VMI standard in Linux kernel 2.6.16 and demonstrated it to the Linux open-source community at the Linux Symposium in Ottawa, Canada. It was clear that the performance gains of paravirtualization could be attained without sacrificing modularity and code cleanliness and that VMI-enabled kernels could run transparently on native machines without any performance impact. Several VMI-style paravirtualization design philosophies were accepted by the Linux community, leading to the development of the paravirt-ops interface in the 2.6.20 mainline kernel. VMware then worked with the Linux community to include VMI in the Linux kernel. Today VMI can be enabled in mainline Linux kernel 2.6.22 and above. See Knowledge base article #1003644 for instructions on how to enable VMI in your custom Linux kernel.

Since VMI-enabled kernels can run on native systems, the popular Linux distributions Ubuntu Feisty Fawn (7.04) and Ubuntu Gutsy Gibbon (7.10) were shipped with VMI enabled by default in the kernel, providing transparent performance benefits when they are run in ESX Server 3.5. VMware is also working with Novell to include VMI in the SUSE Linux Enterprise Server distribution. We in the Performance group did a study to evaluate the performance benefits of using a distribution that supports VMI, the results of which can be found in this whitepaper.

The paper has details on the workloads that we ran, the benchmark methodologies used, and the reasoning behind them. It will be clear from the paper that VMware’s VMI-style paravirtualization offers performance benefits for a wide variety of workloads in a totally transparent way. With support for virtualization techniques like binary translation and hardware assist, and now the addition of VMI paravirtualization, VMware provides customers the most comprehensive range of choices, allowing them to choose the right virtualization technique based on the guest operating system and workload.

You can also learn more about VMI’s performance benefits at my upcoming talk, "VMI: Maximizing Linux virtual machine performance in ESX Server 3.5" at VMworld Europe 2008. I hope to see you there.