Red Hat has launched a beta version of Red Hat Enterprise Linux Version 6.0 with increased power and performance for the KVM hypervisor, greater Linux server scalability and a new version of the Enterprise Linux file system.

The priorities in Version 6 in effect set an expanded agenda for Red Hat Enterprise Linux. "This release sets the scene for the next decade," said Nick Carr, Red Hat marketing director in an interview. The beta release of Version 6.0 became available for download on April 21. General availability will come at an unspecified time later this year.

In version 6.0, a virtual machine running under KVM may have up to 64 CPUs, up from a maximum 16. Red Hat's customers, in their largest virtual machines today, tend to use a maximum of 32 CPUs per virtual machine and 256 GBs of memory. Under KVM in version 6.0, they will be able to use up to a terabyte of memory.

Karr said Red Hat has focused a lot of engineering effort on increasing the I/O throughput of KVM virtual machines. VMs may now invoke single-root I/O virtualization, or SRIOV, which allows them to bypass the hypervisor and send I/O directly to disk drives based on Peripheral Component Interconnect Express (PCIe).

Such a move sidesteps the operation of software switch in the hypervisor, speeding throughput, Carr said. A KVM virtual machine can also send I/O directly to Fibre Channel based storage in the new version.

RHEL 6.0 also includes Kernel Shared Memory, where the KVM hypervisor can identify a page of data in random access memory that's identical to another page, and eliminate one of the duplicates. When an Enterprise Linux server is hosting multiple Windows virtual machines, many of the pages in memory are duplicates, and KVM can share one page across many VMs. Such a move reduces each virtual machine's memory requirement and makes room for more virtual machines on the same host, Carr said.

Another effort to improve overall performance, as well as virtual machine performance, was building in the option of using an increased size of virtual memory pages. With Huge Transparent Memory, Enterprise Linux 6.0 will be able to load pages into memory that contain two megabytes of data instead of being restricted to the current four kilobytes.

The larger pages reduce the number of pointers that map memory pages to real physical memory in the system. Hundreds or thousands of memory pointers fill chip caches when pages are limited to 4 kilobytes each, Carr noted.

These features will make it possible to run heavy I/O servers, such as database servers, in a virtual machine under Linux, Carr predicted. Database systems have not typically been included on the list of virtualized servers in the data center so far.

Version 6 will have all the features of the 2.6.33 version of the Linux kernel in it that Red Hat deems suited for the enterprise, along with backward-compatibility with previous versions of the kernel that Red Hat has used in Enterprise Linux, Carr said. Red Hat picks and chooses what it puts in Enterprise Linux, then maintains support over a minimum of seven years; support for any version is available for up to 10 years at an augmented price.

Linux has lagged the Windows world when it comes to power management, but Version 6 includes many power management features. When there's no I/O going on, active state power management kicks in and reduces the amount of power being supplied to PCI I/O devices.

When software is idling, the kernel allows a "tick-less" state to set where the CPU clock doesn't need to report to the operating system many times a second where it's at in terms of millisecond timing. In some cases, software needs a thousand clock reports or "interrupts" a second, allowing the software to know precisely when to do something. Going to a tick-less state allows reduced power consumption by the chip.

Version 6 will support the ext4 version of the ext file system and makes it the operating system's default setting. It will replace ext3, which has been in operation since 2001-2002 timeframe, Carr said.

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