This minor update releases typically provide feature enhancements, bugfixes and new hardware support. From the release notes:
Highlights of the Red Hat Enterprise Linux 5.5 release include hardware enablement for the Intel Boxboro-EX platform, AMD Magny-Cours processor and IBM Power 7 processor.
Virtualization is improved, with support for multiple 10 GigE SR-IOV cards, and automatic usage of hugepages for virtual guest memory when enabled on the system. Interoperability improvements include boot support for virtual machines using Microsoft based PXE services.
A summary of technical details would highlight:
- Kickstart improvements to logging post-install
- New hardware driver support (pmcraid, ibmvfs, bfa, be2iscsi)
- Updated hardware support (too many to list)
- Run-time memory allocation for KVM guests (memory ballooning)
- PCI passthrough improvements (hotswapping PCI devices, 1:1 performance improvements)
- Detecting kernel tasks stuck in the uninterruptible sleep state (D-state)
- Improved CFQ I/O scheduler performance
- Kernel CIFS updates and new GFS mount option (for troubleshooting)
Apart from this Red Hat also shared Technology Previews within each release. Functionality that is not yet supported, but available for testing purposes:
- FCoE (Fibre Channel over Ethernet)
- ext4 filesystem support
- gcc 4.4 and new glibc malloc
- Trusted Platform Module (TPM) hardware support
- eCryptfs cryptographic filesystem
- Stateless Linux
- SGPIO Support for dmraid
- Device Failure Monitoring of RAID sets
- iSER support (block storage transfer across a network)
The above Technology Preview features of RHEL5.5 may become part of a future RHEL5 release! Even though there is no predicted timeline for CentOS releases, CentOS 5.5 is not expected before May 4th 2010.
For more details on the changelog, please check the release notes here.