Red Hat Enterprise Linux 6 review

Over three years in the making, the intention behind Red Hat Enterprise Linux 6 (RHEL 6) is to equip the flagship Red Hat platform to handle the changing computing demands of its mostly large enterprise customers. As such RHEL 6 boasts major enhancements in terms of scalability, reliability and virtualisation, although they’re not all immediately obvious and one or two may not be to everyone’s liking.

One of the most welcome changes is enhanced support for the latest multi-core processors, Red Hat claiming the ability to handle up to 4,096 cores/threads per system image in RHEL 6 – up from 64 in the previous release. Likewise, the addressable memory limit gets a boost, from 1TB to 64TB should you find a server able to support it.

There’s technology also to identify and quarantine defective memory areas and allow processors and RAM to be added on the fly, albeit only on hardware that allows this kind of component hot-swapping which, again, is rare.

The Anaconda-based install routine has also been updated, making the product a lot easier to deploy. For our tests we installed the server version using a Dell PowerEdge R310 fitted with a quad-core Xeon processor and 16GB of memory.

The whole process took just 15 minutes thanks to the intuitive graphical interface plus the availability of pre-built server configurations as well as the option of customising the setup more individually.

For our tests we chose a virtualisation host configuration to enable us to check out another big change in RHEL 6 – the dropping of Xen virtualisation in favour of KVM (Kernel-based Virtual Machine) using technology, originally from Qumranet, which Red Hat bought back in 2008.

First introduced alongside Xen in RHEL 5.5 (April 2010), KVM is now the sole approved virtualisation platform, a move which could well deter customers upgrading where they already have a significant investment in Xen virtual machines. And that despite the availability of tools to convert Xen VMs to KVM format. That said, however, KVM is a rapidly maturing solution, able to match what Xen can offer in terms of functionality while exceeding its capabilities when it comes to performance.

The RHEL 6 implementation of KVM allows guests to be allocated up to 64 virtual processor cores and 256GB of memory, plus there’s a new SELinux sandbox option so that virtual machines can be run in their own, protected, environments.

Plus there’s a new feature known as KSM (Kernel Samepage Merging), to share identical memory pages across virtual machines and thus minimise overheads and improve performance – memory de-duplication, if you like.

On the downside, KVM isn’t a complete solution in the same way as with VMware or Xen server, for example. Very little in the way of management is built-in on the server side and once we’d installed our server and re-booted, we found ourselves faced with a basic command-line interface which meant having to run the separate virt-manager tool from a RHEL client desktop to configure and manage our VMs.

Easy enough, once we got the hang of it, but it took a while to work out what was needed and is far from the kind of complete solution some buyers might expect.