KVM storage performance and Qcow2 prellocation on RHEL 6.1 and Fedora 16

Written by Gionatan Danti on . Posted in Virtualization

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Some months ago, I wrote an article showing a significant problem regarding KVM and Qcow2 implementations under Red Hat Enterprise Linux 6.0. The problem was that using the default, not-preallocated Qcow2 file backend, I/O performance greatly suffered. You can read here for more information.

Today, I want to see if anything has changed in the last months: more specifically, I am curious to know if manual metadata preallocation remain a necessity or if the underlying Qcow2 / KVM code improved at a point were we can simply forget about manually creating a preallocated Qcow2 file backend.

KVM vs Virtualbox 4.0 performance comparison on RHEL 6

Written by Gionatan Danti on . Posted in Virtualization

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Over one year ago, I tested the then-current versions of KVM, Virtualbox, Xen and VMWare Server in an attempt to identify the best-performing hypervisor (you can find the article here). That tests demonstrated that VMWare Server and Virtualbox where the highest performing softwares, with KVM slightly behind due to slow I/O speed and Xen severely lagging in CPU and memory speed. While the results were surely interesting, I tested the various virtualizer with one guest system only, and I never found the time to run the (desired) multi-guests test.

Now, the free virtualizers landscape is considerably changed: VMWare Server has not been updated since the end of 2009 and now it has some serious problems with the current libc version, while Xen seems a bit “forgotten” by the Linux community. At the same time, KVM and Virtualbox gained considerably traction, and they emerged as the favorite virtualizers in the Linux world.

KVM I/O slowness on RHEL 6

Written by Gionatan Danti on . Posted in Virtualization

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Over one year has passed since my last virtual machine hypervisor comparison so, in the last week, I was preparing an article showing a face to face comparison between RHEL 6 KVM technologies versus Oracle VirtualBox 4.0 product. I spent several days creating some nice, automated script to evaluate these two products under different point of views, and I was quite confident that the benchmark session would be completed without too much trouble. So, I installed Red Hat Enterprise Linux 6 (license courtesy of Red Hat Inc. - thank you guys!) on my workstation and I begin the virtual images installation.

However, the unexpected happened: using KVM, a Windows Server 2008 R2 Foundation installation took almost 3 hours, while normally it should be completed in about 30-45 minutes. Similarly, the installation of the base system anticipating the “real” Debian 6.0 installation took over 5 minutes, when normally it can be completed in about 1 minute. In short: the KVM virtual machines were affected by awfully slow disk I/O subsystem. In previous tests, I saw that KVM I/O subsystem was a bit slower, but not by so much; clearly, something was impairing my KVM I/O speed. I tried different combination of virtualized disk controllers (IDE or VirtIO) and cache settings, but without success. I also changed my physical disk filesystem to EXT3, to avoid any possible, hypothetical EXT4 speed regression, but again with no results: the KVM slow I/O speed problem remained.

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

Written by Gionatan Danti on . Posted in Virtualization

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Today, “Virtual machine” seems to be a magic words in the computer industry. Why? Simply stated, this technology promise better server utilization, better server management, better power efficiency, and, oh yes, some other random pick of better things! The obvious question is if virtual machines technology really provide this better experience. In short: yes. While it has its set of problems and complications, when used correctly this technology can really please you with some great advantages over the one-operating-system-for-one-server paradigm vastly used in the x86 arena.

But, assumed that virtual machines make sense in your environment, what is the best virtualization software to choose? There are many virtualizer and paravirtualizer available today, and some once-commercial virtualization softwares are now freely released (for examples, think to VMware Server and Citrix XenServer). In the end, the choice can be very hard. As the remaining commercial, non-free virtualizator are designed for the upper end of the market (datacenters or large-sized corporates), this article will focus on available, free virtual machine softwares. So, be prepared to a furious battle between VMware vs Virtualbox vs KVM vs Xen!