RHEL 6.1 lays foundation for future servers

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Commercial Linux distributor Red Hat has moved the 6.1 release of its Enterprise Linux from beta to prime time.

RHEL 6.1 is an update to the flagship Linux operating system from Red Hat, which came out in its 6.0 version back in November 2010. The 6.0 version was a major upgrade to the company's Linux OS, with nearly twice as many packages in the stack riding atop of the Linux 2.6.32 kernel, at 2,058 programs; that 6.0 version also had 1,821 feature requests from partners and customers and more than 3,900 enhancements to the Linux kernel contributed by Red Hat software engineers.

The RHEL 6.1 update comes fairly hot on the heels of 6.0, going into beta in late March and now ready for production roll outs here in mid-May. This is in keeping with the six-month cadence that Red Hat likes to have for its releases, Tim Burke, vice president of Linux engineering, tells El Reg.

There were 314 packages updated in the RHEL 6.1 release, and another 49 new packages rolled into the distro. The RHEL 6.1 technical notes have a lot of detail on what has been changed or added.

The 6.1 update includes the usual bug patches and security updates, of course. Red Hat has optimized the processor scheduling algorithms used in NUMA servers, too, and has also fixed some issues with the tickless timer that was recently added to the Linux kernel. But RHEL 6.1 also has some tweaks for hardware, including support for processors, chipsets, and systems that do not yet exist on the market but which are being qualified and tested right now among server makers.

"A lot of the key work in this release is hardware enablement," explains Burke, who says that the new chips and chipsets due within the next nine to twelve months from Intel and Advanced Micro Devices have a lot of scalability and feature enhancements that Red Hat has to be ready to support.

This includes, of course, the SAS disk controller embedded in the Intel "Patsburg" chipset expected with the "Sandy Bridge" Xeon E5 processors due in the third quarter, as well as the "Interlagos" Opteron 6200 processors due from Advanced Micro Devices around the same time. Burke said he could not be specific about all of the new processors and chipset features supported because it would be in violation of non-disclosure agreements.

Red Hat has been given the green light by Intel, however, to talk about support for the hot addition of processors and memory for servers using for Intel's Xeon 7500 processors, the high-end x64 chips announced last year. The hot-add support also extends to the "Westmere-EX" Xeon E7 processors that came out in early April, Burke confirmed, even though the RHEL 6.1 release notes don't say this. The Westmere-EX chips are socket compatible and use the same memory architecture, so it stands to reason hot-adding will work on these newer Xeon E7s as well.

The interesting bit is that servers supporting this hot-addition of CPU and memory modules are not yet on the market, and Burke warns that it won't work on just any old system. The link between RHEL and the system BIOS has to be very tight to allow this capability.

Various network and storage peripheral cards have new or updated drivers, too, with emphasis on improving the performance of the Fibre Channel over Ethernet (FCoE) protocol used for converged server-storage switching on 10 Gigabit Ethernet switches; there are also improvements for data center bridging and iSCSI offload to make network storage perform better.

The idea, says Burke, is to use data center bridging to provide dedicated bandwidth – and hence guaranteed quality of service for data – on links between servers and iSCSI disk arrays. RHEL 6.1 also has a lot of additions and tweaks for converged network adapter cards, and has early support for 40 Gigabit Ethernet and FDR (56Gb/sec) InfiniBand adapters.

There are a lot of tweaks in the KVM virtualization stack, as you might expect, but not on the scalability front. Burke says that the current scalability limits for a guest operating system on a KVM hypervisor – up to 64 physical cores and up to 512GB of memory – is more than sufficient. But Red Hat's software engineers have done some work under the covers to make the overhead lower for guests. Specifically, with RHEL 6.1, a lot of the network handling functions have been moved from the QEMU emulator that sits underneath KVM and down into the kernel space. Burke says that on typical workloads, this can boost performance around 5 per cent.

There are also a number of technical previews of software that is not quite ready for prime time, but which Red Hat wants customers to get early access to so they can provide feedback before it gets cooked into the RHEL stack proper. RHEL 6.1 offers a tech preview of the XFS file system used in clusters using the High Availability Add On for the operating system, plus experimental support for the BTRFS file system.

There is also a tech preview of FS-Cache, which provides a persistent cache for NFS; a TPM feature, which allows RHEL 6 to create, store, and use RSA keys without storing them in main memory; and Linux Containers (LXC), which is another resource management and isolation mechanism to complement virtual machine partitions and to provide a userspace container for applications and systems.

Red Hat is also debuting the first stage in a multi-release rollout of an as-yet unnamed new subscription management feature that will make it easier for companies to keep track of their RHEL licenses separately from Red Hat Network. The idea is to allow customers to do internal license compliance checking, and the idea is coming from customers, not Red Hat.

The pricing and packaging of RHEL 6 remains the same with the RHEL 6.1 release, and no one is forced to upgrade to it to stay on support, of course. El Reg walked you through the ins and outs of RHEL 6 pricing back in November. ®

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