Vmware vs Virtualbox vs KVM vs XEN: virtual machines performance comparison

Written by Gionatan Danti on . Posted in Virtualization

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I/O benchmarks: HDTune benchmark

The second test is HD Tune Benchmark Pro, which let us examine the bandwidth and access time of the primary disk reading 512 byte, 4 KB, 64 KB and 1024 KB sized chunks. Generally, the low-sized fragment benchmarks are access-time bound, while the 1024 KB sized benchmark is peak bandwidth bound.

Let see the results (please keep in mind that the HDTune benchmarks are read only tests):

HDTune read bandwidth

Can you ever see the 512 byte and 4 KB results? This graph is typical for a server equipped with mechanical disks: the lowest-sized benchmarks are dominated by seek time (which is a constant time, not related to chunk size). This is the main reason while flash-based SSD are so fast ;)

However we can isolate the virtualizer speed, and we can see that Xen and KVM are considerably slower that Vmware, which in turn is slight slower that VirtualBox across the board. Another point of view for the same that is the following:

HDTune read IOPS

This time, we are not measuring performances on KB/s, but on IOPS (I/O operations per second) terms. As you can see, VirtualBox satisfies the greater number of IOPS for the three low sized benchmark, while it is only slight behind the leader (VMware) on the 1024 KB sized test.

At last, we want to see the disks total access time (seek time + read latency)

HDTune access time

This graph is yet another view of the same data: VirtualBox is the leader shortly followed by VMware, while KVM and especially Xen are significantly slower.

Did you remember that I run that test invalidating host-side cache each time? What can be the I/O results if we did not that action and, instead, we want to use the host-side cache? If you are curious, these graphs are for you...

Bandwidth results:

HDTune cached bandwidth

I/O operations per second:

HDTune cached IOPS

Access time speed:

HDTune cached access time

Wow, if a real physical disk can really guarantee that sort of results, it should be a best buy ;)

Seriously speaking, these results are not really from the physical disk subsystems: they are a cache-to-cache copy or, if you prefer, a host-memory-to-guest-memory copy. In other words, these results really shown hypervisor's I/O overhead.

VMware is the indisputable leader, with VirtualBox at the second place and Xen, greatly behind, at the third. The most interesting thing however is the incredibly slow KVM shown: its results are only a little better that the non-cached version. What can be the culprit here? The cache was disabled? I think no, because the results are better than the non-cached version – they are only too little better. It can be the slow block subsystem? Yes, it can be, but the 1024 KB seems to suggest a slow host-to-guest memory copy performance also. Whichever is the cause, KVM is simply a full light-year behind in the cached tests.

UPDATE: a recent article comparing KVM vs VirtualBox can be found here: http://www.ilsistemista.net/index.php/virtualization/12-kvm-vs-virtualbox-40-on-rhel-6.html


#1 Nathan 2012-09-12 03:12
This is a terrible review, to install the VMware paravirtual drivers but not the KVM Windows paravirtual drivers. All results from VMware must be discarded for comparison purposes.
#2 Marcelo 2015-11-15 03:16
A quick comparison I made between VMware Workstation Player and VirtualBox, with XP as guest, shows a ridiculous I/O advantage of VB, while VMware has a big advantage on 3D graphics.
#3 Gionatan Danti 2015-11-15 09:32
Quoting Marcelo:
A quick comparison I made between VMware Workstation Player and VirtualBox, with XP as guest, shows a ridiculous I/O advantage of VB, while VMware has a big advantage on 3D graphics.

Hi Marcelo,
VBox higher I/O speed probably is an artifact of VBox not honoring write barrier (synchronized writes) by default. While this give much higher speed, storage consistency is somewhat reduced and I do not suggest to disable write barriers on production host/machines.

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