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RHEL 6 gets its first beta

Massive scale, less virty overhead

Interestingly, the tickless kernel that made its debut in Red Hat Enterprise MRG - the messaging, real-time, grid variant of RHEL aimed at high performance computing customers - is mainstreamed with RHEL 6. So companies won't have to buy the MRG variant to get this feature. However, Burke says that MRG will continue to be a distinct distro from Red Hat, since there will always be some customers where network latency or interrupt handlers are an issue. Exactly what might be in this RHEL 6 MRG product, Burke would not say.

There are a number of interesting features to boost the performance of applications running in virtualized mode. For instance, RHEL 6 includes a feature called transparent huge tables, which takes the concept of huge page memory support that has been around forever on physical servers to boost the performance of databases. In virtualized environments, huge pages were not supported in guests at first, and then when it was brought in, they had to be configured at boot time to preserve memory for the huge pages. Now, the KVM hypervisor can transparently configure huge as well as small or large memory pages as applications running in its guests need. This removes a barrier to the performance of virtualized databases.

Ditto for the networking stack. According to Burke, the way the virtualized networking stack was implemented in RHEL 5, the QEMU emulation layer of KVM hosted the networking stack, but with RHEL 6, a lot more of the networking code has been pushed down into the kernel, so physical and virtual machines have equal access to the features and, more importantly, equal performance. Similarly, the Asynchronous I/O support that has been in Linux for years has been reworked and has a more complete set of features.

"The point is, you no longer pay the virtualization overhead," says Burke.

RHEL 6 includes the ext4 file system as its default, and with the new version it will be able to scale to 16 TB file systems. The important new change with this implementation of ext4, says Burke, is that there is an improvement by many orders of magnitude in the file system recovery time in the event of a crash. It used to take hours to recover a file system on ext4, but now a 16 TB file system can recover itself in a matter of minutes. Red Hat is also making the XFS file system part of the RHEL 6 stack for customers who need to support very large file and directory sizes. NFSv4 is also tossed in, which supports the IPv6 network protocol.

Network block storage is also supported through the FCoE and iSCSI protocols, and LVM/DM volume managers now can resize mirrored and multipathed volumes on the fly. Intel, Cisco Systems, and IBM have done a lot of work on the FCoE drivers along with Red Hat, and they now include topology awareness commands that allow RHEL 6 to ask storage arrays what their optimum chunk sizes and file system specs should be and then pass this information up to virtualized guests and databases to optimize the performance of the software against the specific storage software.

On the RAS front, RHEL 6 has been tweaked to add support for hot-adding of CPUs and memory where the new hardware supports it, and adds hardware checksums for data moving from an application through the system out to disk storage using a feature called DIF/DIX.

RHEL 6 will go through a number of betas and release candidates before being officially launched. How many depending on tester feedback. But if history is any guide, it should take five or six months for RHEL 6 to get fully baked.

RHEL 6 will be available in both server and desktop variants, and you can take the first beta for a spin here. ®

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