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21 June 2012, 16:56
RHEL 6.3

What's new in Red Hat Enterprise Linux 6.3

Thorsten Leemhuis

Like many other recent Red Hat minor releases, the third update of RHEL 6 focuses mainly on virtualisation improvements.

In line with its six-monthly release schedule for minor updates of Red Hat Enterprise Linux, Red Hat has now released RHEL 6.3. As RHEL 6 is still in the first phase of its life cycle, the Linux distribution's third update contains a variety of improvements and new features, as well as recent bug fixes.

For example, RHEL 6.3 officially supports allocating up to 160 processor cores and 2TB of working memory to guest systems; previously, the distribution only supported 64 cores and 512GB of RAM. Spice, which is involved in virtualising desktop PCs, can now pass through USB 2.0 devices from the system that is displaying the desktop to a local or remote virtualised guest operating system. Another new feature is support for SR-IOV-capable (Single Root I/O Virtualisation) networking hardware which can present a single physical card as multiple, separate virtual network cards; this support allows these virtual network cards to be allocated to guest systems.

The new "dynamic virtual CPU allocation" (aka "vCPU hot plug") feature allows the number of CPU cores that are allocated to a guest system to be increased at runtime; reducing the number is not yet possible. This feature is still classified as a Technology Preview and is, therefore, not covered by Red Hat's support. The same applies to Virtio-Scsi which, like Virtio-Blk, allows devices to be emulated via Qemu so that data can be transferred between hosts and guests with very little overhead; however, Virtio-Scsi, which has also been integrated into Linux 3.4, is designed to pass through more than 25 devices and can apparently also pass through SCSI devices from the host to the guest via the "scsi-block" QEMU device.

RHEL 6.3 is the first version to offer the Virt-P2V ISO image. This image is used to create bootable CDs and USB flash drives that include the identically named tool; this bootable media can be used to migrate the system storage devices of Windows or RHEL systems that are installed directly on the hardware to an image and adjust them in such a way that these operating systems can then run as KVM guests under RHEL or RHEV (Red Hat Enterprise Virtualisation).


The RHEL kernel's Device Mapper, which is used by the Logical Volume Manager, now offers the Thin Provisioning features that were integrated in Linux 3.2 – it can, therefore, export more storage space than is actually available. This is the basis for a new snapshot feature that is designed to offer better scalability and be more efficient in terms of storage; it also provides the option to create snapshots of snapshots. Both features are still classified as RHEL Technology Previews.

With version 6.3, operation as a SCSI target via Fibre Channel over Ethernet (FCoE) has ceased to be a Technology Preview. Also new are features that allow RAID levels 4, 5, and 6 to be implemented via the Logical Volume Manager (LVM); to do so, LVM accesses the kernel's software RAID code, which is typically managed via Mdadm.


  • The RHEL 6.3 kernel contains the Net_prio Cgroup controller that was integrated in Linux 3.3; administrators can use this technology, which is also known as Network Priority Cgroup Infrastructure, to set network interface priorities for Control Group (Cgroup) processes.
  • The new "numad" background service, which is currently a Technology Preview, is designed to optimise the use of system resources in systems with a non-uniform memory architecture.
  • The SSH daemon can now request multiple types of authentication from users – not just either a password or a public key, but both. Further additions include new centralised administration features for SSH keys.
  • As an alternative to OpenJDK 6, Red Hat has included OpenJDK 7 as a Technology Preview.
  • MySQL's InnoDB plugin can now be used on x86-64 systems; the plugin is said to offer a greater number of features and better performance than MySQL's integrated InnoDB storage engine.
  • Rsylogd has made a version jump to series 5.
  • The system's Linux Container (LXC) support, and the Btrfs filesystem that is still considered experimental in kernels, continue to be classified as Technology Previews in RHEL 6.3; Oracle and SUSE have officially supported both technologies in their own enterprise distributions for about three months.


As usual, Red Hat has integrated various new drivers and updated dozens of existing ones. For example, the Bnx2x network driver has been updated to version 7.2.16 and supports Broadcom's 578xx family of network components; the Enic driver for 10G Ethernet chips by Cisco offers SR-IOV, and the Iwlwifi driver for Wi-Fi components by Intel can now communicate with the Centrino Wireless-N 6235 series of Wi-Fi chips. A new addition is the Mtip32xx storage driver for RealSSD P320h PCIe SSD drives by Micron.

The Linux distributors have also updated many other storage drivers and the Alsa audio drivers. The DRM drivers have been updated and are now roughly equivalent to the graphics drivers in the second release candidate of Linux 3.3. New in RHEL 6.3 is the RDRAND x86 instruction support that was integrated into Linux 3.2 to support random number generators such as those included in Intel's Ivy Bridge CPUs.

The release notes list the version status of many other drivers and explain numerous other new RHEL 6.3 features. Further background information and technical details can be found in the technical notes and in other RHEL 6 documents.

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