Red Hat drops Xen from RHEL

IDG News Service - With Wednesday's beta release of its flagship operating system, Red Hat Enterprise Linux (RHEL), Red Hat has added a number of new capabilities that should help data centers better support virtualization and cloud computing.

RHEL 6.0 will also have at least one less feature as well. This will be the first version of the OS not to include the Xen hypervisor. Instead the company plans to focus its virtualization efforts around the kernel-based Virtual Machine (KVM), said Tim Burke, Red Hat vice president of platform engineering.

For RHEL 6, "Virtualization has been a key focus, as has providing infrastructure that will be part of our cloud services," Burke said.

To help in cloud deployments, the RHEL 6 OS has the ability to dynamically allocate kernel data structures. "This will allow cloud service providers to give better service-level agreements," Burke said. As virtual machines are loaded on to the OS, the administrator can specify how much memory, how many processing cycles and how much network bandwidth can be allotted to each machine.

Another new addition is the Completely Fair Scheduler (CFS), which "more dynamically balances the workloads among the tasks," distributing the CPU resources more evenly across all the applications. Borrowing techniques from Red Hat's software for running latency-intolerant services, it also does a more sophisticated job of scheduling high-priority processes over low-priority ones, Burke said.

Power savings features have been added. The timing infrastructure has been reorganized as well, and uses something called the tickless kernel enhancement. Previously, the kernel would interrupt the CPU 1,000 times per second to take a time measurement, which prevented the CPU going into power-saving sleep mode. The tickless kernel feature relies instead on hardware-based timers, allowing the CPU to go to sleep in those periods when there are no other chores to complete.

The file systems space has been revamped for larger data sets. This is the first version of RHEL to use ext4 as the default file system. (Formerly it used ext3.) RHEL can now run file systems of up to 16 terabytes. The new file system also runs file system checks much more speedily, which means faster recovery times after unclean shutdowns. For really big data sets, RHEL also includes an option to upgrade to SGI's XFS file system, which can scale to 128 terabytes.

With Red Hat's emphasis on supporting cloud computing, the company's decision to drop Xen may seem surprising. But over the past few years, Red Hat has increasingly thrown its support behind KVM. In 2008, the company purchased virtualization software provider Qumranet, whose developers pioneered much of the early KVM work.