Linux distributions tend to fall into one of two camps. The first are those, like Ubuntu and Fedora, that are aimed mostly at enthusiasts and others happy to teeter on the bleeding edge of technology. The other group consists of more stable, commercially supported software, designed for those after less excitement, and includes products such as SUSE Linux Enterprise and Red Hat Enterprise Linux (RHEL). New releases are a rarity in this category, so when a major new product like RHEL 6 comes along it’s a big event, and one worthy of close attention.
It has been three and half years since the last big Red Hat release (RHEL 5), and the first thing to say is that customers aren’t expected to all rush out and upgrade. Indeed, RHEL 5 will continue to be supported for several years yet, with plenty of good reasons for staying put – at least in the short term.
The most pressing has to be the dropping of Xen virtualisation in favour of KVM (Kernel-based Virtual Machine) technology in the new release – a long anticipated move following Red Hat’s acquisition of KVM developer Qumranet, back in 2008. A key component of RHEL 5.5, and now fully integrated into version 6, KVM delivers what most users need when it comes to a virtualisation platform. However, existing Xen users are likely to be reluctant to switch from what is seen as a much more mature solution, even though a tool to convert Xen VMs to KVM format is included.
On the plus side, KVM is now functionally on a par with the Xen platform with the added benefit of performance enhancements in the RHEL 6 release, plus an SELinux sandbox option to enable virtual machines to be run in their own, isolated, environments. Red Hat has also added a new feature known as KSM (Kernel Samepage Merging), effectively a de-duplication of memory to enable identical memory pages to be shared across virtual machines, minimising overheads and improving performance.
Beyond KVM there are several other big enhancements to tempt both buyers and upgraders alike, particularly when it comes to multi-core processor support and memory scalability. The theoretical bar is now set at an impressive 64,000 cores, although the supported limit is a more conservative 4,096 cores with up to 64TB of addressable memory – still a big leap compared to just 64 cores and 1TB of RAM in RHEL 5.
VM limits are also bumped upwards, with KVM guests able to handle 64 cores and 256GB of memory.
Naturally there’s a new Linux kernel in this release, Red Hat now employing v2.6.32, albeit with a few later tweaks of its own, while EXT4 is now the default file system rather than the EXT3 used before. That said, you’re still limited to just 16TB of storage even using EXT4. Customers who are looking to support more than that will have to buy the so-called Scalable File System add-on, which uses the XFS journaling file system to support up to 100TB.
Support for Fibre Channel over Ethernet (FCoE) has also been added, and iSCSI SAN technology enhanced to enable iSCSI partitions to be used as root or boot devices. Resilient storage and more general high-availability add-ons are also available to further enhance storage and other core capabilities within the RHEL 6 platform.
Available for both workstation and server use, we found both versions of Red Hat equally easy to install using the graphical installer provided. A choice of pre-configured setups makes the process very straightforward, both with older server hardware and the latest in desktop and notebook technology. On the downside, we did have to search out proprietary drivers for some desktop graphics chipsets and download other add-ons to handle multimedia playback, but dual-screen support in this release is much better than in previous versions. Useful power management enhancements are also included as standard. Printer support is a lot better too, with automated setup in many cases.
In terms of the look and feel, little appears to have changed at first. Gnome remains the default desktop environment, although the underlying version is now 2.28. Desktop users also get OpenOffice 3.2 and the Firefox 3.6 browser, while the flood of add-on applications typically bundled with other Linux distros is reduced to a trickle in RHEL 6 – presumably reflecting the more conservative needs of enterprise customers. That said, many of the missing packages can be added from the aptly named EPEL (Extra Packages for Enterprise Linux) repository using the Yum and PackageKit tools provided.
Server buyers, meanwhile, get the usual LAMP stack, comprising Apache 2, MySQL 5 and Perl 5.10. A plethora of performance and management enhancements have also been implemented, including a new System Security Services Daemon (SSSD) for central identity management.
RHEL isn’t free in the same way as with some Linux distros. Red Hat effectively charges to use its product via a variety of subscription-based support contracts. Desktop contracts start at $49/year (£32 + VAT) while server contracts can be had from just $349/year (£224 + VAT), both on a self-supported basis. It’s worth noting, however, that with RHEL 6, server licences are per CPU socket pair, rather than covering the whole server as with the previous release. Moreover, virtualisation support beyond a single virtual guest costs extra, as do the various optional performance and availability add-ons – and these can seriously rack up the overall cost for larger enterprises.
Some three years in the making, the latest release of Red Hat Enterprise Linux appears at first glance conservative. Dig a little deeper, though, and you’ll find performance and scalability enhancements to cope with the latest multi-core processors, plus the ability to handle up to 64TB of RAM. There are big changes too when it comes to storage plus high availability and other optional add-ons. Xen virtualisation is dropped in favour of KVM, which could deter some from upgrading. Overall, though, it’s a well implemented and supported enterprise Linux release, and one that should keep Red Hat customers happy for many years to come.
Company: Red Hat
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