LXD crushes KVM in density and speed

  • LXD achieves 14.5 times greater density than KVM
  • LXD launches instances 94% faster than KVM
  • LXD provides 57% less latency than KVM

LXD is the container-based hypervisor lead by Canonical. Today, Canonical published benchmarks showing that LXD runs guest machines 14.5 times more densely and with 57% less latency than KVM.

The container-based LXD is a dramatic improvement on traditional
virtualisation and particularly valuable for large hosting environments.
Web applications, for example, can be hosted on a fraction of the
hardware using LXD than KVM resulting in substantial long term savings
for large organisations.

Latency-sensitive workloads like voice or video transcode showed 57%
less latency under LXD than KVM, making LXD an important new tool in the
move to network function virtualisation in telecommunications and
media, and the convergence of cloud and high performance computing.

Mark Shuttleworth announced the results at the OpenStack Developer
Summit in Vancouver, Canada, saying “LXD crushes traditional
virtualisation for common enterprise environments, where density and raw
performance are the primary concerns. Canonical is taking containers to
the level of a full hypervisor, with guarantees of CPU, RAM, I/O and
latency backed by silicon and the latest Ubuntu kernels.”

The introduction of containers in Linux by the
project, lead by Canonical, has sparked a series of disruptions such as
Docker for application distribution, culminating in the recent
introduction by Canonical of LXD, which behaves exactly like a full
hypervisor but eliminates the overhead of virtualization or machine
emulation. While LXD is only suitable for Linux workloads, the majority
of guests in OpenStack environments are Linux, making LXD a compelling
choice for private clouds where efficiency is highly valued.

Early adopters include institutions with many Linux virtual machines
running common code such as Tomcat applications under low load. LXD
offers much higher density than KVM as the underlying hypervisor can
consolidate common processes more efficiently. LXD’s density comes from
the fact that the same kernel is managing all the workload processes, as
does its improved latency and quality of service.

Ubuntu is the most popular platform for large-scale KVM
virtualisation and the most widely used platform for production
OpenStack deployments. “We will of course continue to improve KVM in
Ubuntu, but we are extremely excited to enable LXD alongside it for
guests where raw performance, density or latency are of particular
importance,” said Mark Baker, product manager for OpenStack at

The testing

The target platform for this analysis was an Intel server running
Ubuntu 14.04 LTS. The testing involved launching as many guest instances
as possible with competing hypervisor technologies, LXD and KVM.


In the density test, an automated framework continually launched
instances while checking hypervisor resources and stopped when resources
were depleted. The same test was used for LXD and KVM; only the command
line tool used to launch the images was different.

The server with 16GB of RAM was able to launch 37 KVM guests, and 536
identical LXD guests. Each guest was a full Ubuntu system that was able
to respond on the network. While LXD cannot magically create additional
CPU resources, it can use memory much more efficiently than KVM. For
idle or low load workloads, this gives a density improvement of 1450%,
or nearly 15 times more density than KVM.


Containers utilize resources more efficiently at steady-state after
booting. As a result, there is a dramatic improvement in the number of
instances that can be packed onto a single server providing significant
cost benefits due to more efficient utilization of resources.


Not only did the test show that LXD could launch and sustain 14.5x
the guests than KVM, it also starkly highlighted the difference in
startup performance between the two technologies. The full 536 guests
started with LXD in substantially less time than it took KVM to launch
its 37 guests. On average, LXD guests started in 1.5 seconds, while KVM
guests took 25 seconds to start.



LXD’s container approach lets performance critical applications run
at bare metal performance while retaining the isolation of workloads and
the ability to support a wide range of Linux operating systems as
guests. Without the emulation of a virtual machine, LXD avoids the
scheduling latencies and other performance hazards often found in
virtualization. Using a sample 0MQ workload, testing resulted in 57%
less latency for guests under LXD in comparison to KVM.


More information about LXD can be found at

Canonical is exhibiting at OpenStack Summit, Vancouver. Visit booth P3 for further details and to meet the team.

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