Btrfs ready for production in new Oracle Linux kernel
In "release 2" of the "Unbreakable Enterprise Kernel" (UEK), which is intended for Oracle Linux from versions 5.8 and 6.2, Oracle has called the Btrfs filesystem "production-ready". This makes Oracle the second Linux distributor to officially support Btrfs in an enterprise distribution, even though the filesystem is currently still considered experimental in the Linux kernel that is maintained by Linus Torvalds. SUSE took this step in late February with the second service pack for SUSE Linux Enterprise (SLE), which is the first version where the use of the designated "Next Generation File System" is covered by the SUSE support.
In Fedora, OpenSUSE and Ubuntu, Btrfs has been available during installation for some time. However, plans to use Btrfs as the default filesystem have repeatedly been postponed; one of the reasons is that only a rudimentary tool for testing and repairing Btrfs filesystems is available. Like SUSE, Oracle's distribution includes an improved variant of the btrfsfsck program that hasn't become available separately. The code for an improved test and repair tool has been available in the developer repository for Btrfs tools for a month – but it is located in a branch whose name, "dangerdonteveruse", clearly advises against its use.
Oracle says that, like the first Unbreakable Enterprise Kernel, the second release offers better scalability and performance than the non-UEK kernels of Oracle Linux – like most other Oracle Linux components, they are clones of the Red Hat Enterprise Linux (RHEL) source code packages. While the RHEL 6 kernel and the first UEK kernel were based on Linux 2.6.32, the UEK R2 kernel is based on Linux 3.0.16; as the leading "3" and the shorter version number can confuse certain programs, the kernel identifies itself as 2.6.39.
Using a kernel base that is about 18 months newer allows the UEK R2 kernel to offer all the features that were added to the official Linux kernel during that time; new additions include Transparent Huge Pages (THP), memory compaction, transmit packet steering and a range of updated drivers. However, some of these and other features can also be found in the 2.6.32-based RHEL 6.2 kernel and in its Oracle Linux 6 clone.
Oracle also points out that the new kernel offers improved Xen support. Furthermore, the kernel includes several new features that are still considered "technology previews" and are not yet covered by Oracle's support; among these are the DRBD replication solution, the LXC container virtualisation feature, and Dtrace, a tracing component that was originally part of Solaris.
The UEK R2 kernel sources and the changes made by Oracle can be accessed from a Git repository. The release notes discuss the kernel's new features in detail; another document offers a less technical description. The kernel's installation is explained in "Getting Started with Oracle Unbreakable Enterprise Kernel Release 2"; the kernel can also be installed via public Yum repositories, which should allow adventurous users to include the kernel in RHEL and in RHEL clones such as CentOS and Scientific Linux.
Oracle plans to discontinue its support of the first Unbreakable Enterprise Kernel in nine months. No further new hardware support will be added to the first release; instead, Oracle says that it will include such improvements in the UEK R2 kernel updates that it plans to release on a quarterly basis.