Red Hat Enterprise Linux 6
by Thorsten Leemhuis
In the new version 6 of its flagship product, Red Hat has incorporated many technological developments of the past few years. Compared to its predecessor, this release of Red Hat Enterprise Linux therefore contains a large number of changes.
Enterprise distributions of Linux have different requirements than community distributions: not frequent releases, but long-term support and stable, mature technologies are what's needed. While Fedora, Ubuntu and similar distributions release new versions every six months to bring technological advancements to the desktops of Linux fans, Red Hat has allowed three-and-a-half years for the development of Red Hat Enterprise Linux 6. The new version is a major leap forward for Red Hat's main product and offers numerous advancements.
In terms of virtualisation, Red Hat now relies exclusively on KVM (Kernel-based Virtual Machine) as its hypervisor. With this decision, the company has moved one step closer to its long-term goal of saying good-bye to Xen, which was the preferred virtualisation component when RHEL 5 was introduced in March 2007. In 2009, KVM was added as a second hypervisor to RHEL 5.4 after Red Hat took over Qumranet, the company behind KVM. However, Red Hat will continue to support Xen within series 5, which will be maintained at least until 2014.
Unlike Xen, KVM is unable to paravirtualise entire operating systems and relies on processors with virtualisation support – nowadays these can even be found in many budget desktop and notebook CPUs. The younger KVM has now drawn level with Xen's functionality and performance in many areas; in addition, it offers various functions that are not available in Xen. The performance of RHEL 6 guests virtualised with KVM is said to be close to that achieved when RHEL is run directly on the hardware. A tool allows administrators to convert Xen guests implemented under RHEL 5 for operation with KVM under RHEL 6.
Also new is the Kernel Samepage Merging (KSM) feature, which merges identical memory areas of different processes – this can noticeably reduce the host's memory consumption when several KVM guests run the same operating system and applications, or when a lot of memory is left unused. Faster network throughput is in store for guest systems via such technologies as macvtap (speeds up data transfers between guest systems), vhost-net (provides efficient access to the network hardware from the guest) and SR-IOV (Single Root I/O Virtualisation and Sharing Specification).