REVIEW: Red Hat Enterprise Linux 6

Windows isn’t the only fish in the operating system sea, with plenty of companies willing to consider open source Linux alternatives, if not on the desktop—at least when it comes to servers. Even in the corporate datacentre, where Red Hat Enterprise Linux (RHEL) is commonly to be found hosting production systems and giving the Windows Server platform a run for its money.

What is it and who is it for?

The majority of Linux distributions (distros for short) are aimed at enthusiasts and others happy to teeter on the bleeding edge of technology. Distros such as Ubuntu and Fedora, for example, where new releases come along every few months. Business users, by contrast, favour more stable, commercially supported, products, with Red Hat the number one vendor in this market and Red Hat Enterprise Linux (RHEL) its core platform.

The latest release (RHEL 6) has taken some three years to come to fruition, but that’s the way its corporate customers like it. After all, major upgrades can be very disruptive and it’s not as though there haven’t been interim updates since RHEL 5 was introduced back in 2007, the most recent—RHEL 5.5—just under a year ago.

This new version, however, moves the product on a lot further, addressing many of the underlying scalability issues of the Red Hat platform. Most notably enabling it to better exploit what the latest multi-core processor technologies have to offer. OK, it’s not quite as cutting-edge as Fedora, on which the product is based, but it is a big leap forward while, for those still not brave enough, the company remains committed to support for earlier versions while, at the same time, extending support for this new release to 10 years.

RHEL-6_2

Pricing & setup

Although open source, RHEL is far from a free, no-strings attached, distro. Rather, customers can only deploy the product if they take out a commercial update and support subscription, with a number of changes to the way these are priced in this release.

Subscriptions for servers and desktops PCs are still available, with desktop subscriptions starting at £32 (ex. VAT, per year) and servers £225 (ex. VAT, per year), albeit on a ‘self-supported’ basis. The ability to get help from Red Hat (by phone and email) pushes servers up to £515 (ex. VAT, per year) with all-singing, all-dancing, premium server subs starting at £837 (ex. VAT, per year).

Previous standard and advanced server options have been dropped and licenses now applied per pair of processor sockets, rather than covering the entire server. Likewise the basic fee is changed to only include one virtual guest, so customers with more processors or larger VM requirements should expect to pay a great deal more. A 4-socket standard subscription with unlimited guests, for example, is listed at £2,579 (ex. VAT, per year).

Having paid for the subscription the software is available for 32-bit and 64-bit Intel/AMD platforms, plus IBM Power and System Z mainframes. An Anaconda-based setup routine takes care of the installation with, on servers, a number of pre-built configurations to help speed the process.

We had few problems with the install, even with older hardware. However, on recent desktops and laptops we did have to search out proprietary drivers for some of the video and sound cards. On the plus side, dual-screen support is much enhanced in this release, as are the power management and printer options.

RHEL-6_3

Does it do it well?

When it comes to new features, there are two headline grabbers—greater scalability and a sea-change in the preferred virtualisation technology. First the scalability, with claims here (in theory) to support more than 64,000 processor cores which, if the hardware to go with it were available, would be ground breaking. However, it’s not, so the officially quoted limits are more modest at 4,096 cores/threads per system image.

Still, that’s a big increase on the 64 cores supported by RHEL 5 with an associated increase in addressable memory—up from 1TB to 64TB. Bear in mind too that, when more scalable hardware comes along, these numbers will rise without the need for any extra updates. Added to which RHEL 6 comes ready-equipped to add processors and RAM on the fly, again, assuming the hardware to support it.

And then there’s virtualisation, where the big news is the dropping of Xen in favour of KVM (Kernel-based Virtual Machine) technology. Not that big a surprise, given the acquisition of KVM developer, Qumranet, by Red Hat in 2008 and the bundling of KVM as part of the RHEL 5.5 update.

In RHEL 6, however, Red Hat clearly sees KVM as able to match what the more mature Xen technology has to offer, especially in terms of performance. There are security advantages too, such as the ability to share memory pages across VMs (Kernel Samepage Merging), and a new SELinux sandbox to enable virtual machines to run in their own, protected, environments

Beyond these headline changes there’s also the inevitable kernel update (to v2.6.32), updates to just about every other components, and a switch to EXT4 as the default file system. Support for Fibre Channel over Ethernet (FCoE) has also been added to keep pace with what storage vendors have been doing and the iSCSI SAN drivers enhanced to boot the OS from iSCSI partitions.

RHEL-6_4

Where does it disappoint?

The switch to KVM for virtualisation is something of a double-edged sword. As the name implies the technology is implemented in the kernel, with benefits in terms of both VM performance and security. However, customers with existing Xen virtual machines may not welcome having to convert format in order to take advantage of these benefits. A conversion utility is included, but a lack of management tools could also make customers thinks twice before upgrading.

The new EXT4 file system also has the same 16TB limit as the previous EXT3 system, which means having to subscribe to a new chargeable add-on (the Scalable File System) to exceed this using the XFS journaling file system. Similarly, those wanting guaranteed storage availability will have to pay for the Resilient Storage add-on, with a number of other options now separated out of the package as add-on extras.

In its favour, this move makes such options available to all customers, regardless of base subscription, which wasn’t the case before. Against, the add-on model adds to the cost for what, many will see as options which ought to be included as standard.

Would we recommend it?

There’s little doubting that this new release of RHEL is a worthwhile investment, enabling customers to take full advantage of the latest multi-core hardware with the promise of even greater scalability in the future. New buyers and those deploying new servers should certainly have no hesitation in choosing RHEL 6 to host their Linux applications. Whether it’s worth rushing out and upgrading existing systems is less clear cut. Especially, for customers with large numbers of Xen virtual machines who may prefer to wait a while before going through the pain of migrating to the new KVM technology in this release.

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