- EXT3 Enhancement
The maximum capacity of the EXT3 is now 16TB (increased from 8TB). This enhancement was originally included in Red Hat Enterprise Linux 5 as a Technology Preview, and is now fully supported in this update.
- yum-security
It is now possible to limit yum to install security updates only. To do so, simply install the yum-security plugin and run the following command:
yum update --security
- Restarting a Resource Independently
It is now possible to restart a resource in a cluster without interrupting its parent service. This can be configured in /etc/cluster/cluster.conf on a running node using the __independent_subtree="1" attribute to tag a resource as independent.
For example:
<service name="example">
<fs name="One" __independent_subtree="1" ...>
<nfsexport ...>
<nfsclient .../>
</nfsexport>
</fs>
<fs name="Two" ...>
<nfsexport ...>
<nfsclient .../>
</nfsexport>
<script name="Database" .../>
</fs>
<ip/>
</service>
Here, two file system resources are used: One and Two. If One fails, it is restarted without interrupting Two. If Two fails, all components (One, children of One and children of Two) are restarted. At no given time are Two and its children dependent on any resource provided by One.
Note that Samba requires a specific service structure, and as such it cannot be used in a service with independent subtrees. This is also true for several other resources, so use the __independent_subtree="1" attribute with caution.
- Virtualization
The following Virtualization updates are also included in this release:
The virtualized kernel can now use the kdump function.
AMD-V is now supported in this release. This enables live domain migration for fully virtualized guests.
The virtualized kernel can now support up to 256GB of RAM.
The in-kernel socket API is now expanded. This was done to fix a bug that occurs when running sctp between guests.
Virtual networking is now part of libvirt, the virtualization library. libvirt has a set of commands that sets up a virtual NAT/router and private network for all local guests on a machine. This is especially useful for guests that do not need to be routable from the outside. It is also useful for developers who use Virtualization on laptops.
Note that the virtual networking capability adds a dependency on dnsmasq, which handles dhcp for the virtual network.
libvirt can now manage inactive virtual machines. libvirt does this by defining and undefining domains without stopping or starting them. This functionality is similar to the virsh define and virsh undefine commands.
This enhancement allows the Red Hat Virtual Machine Manager to display all available guests. This allows you to start these guests directly from the GUI.
Installing the kernel-xen package no longer leads to the creation of incorrect / incomplete elilo.conf entries.
Fully virtualized guests now support live migration.
The xm create command now has a graphical equivalent in virt-manager.
Nested Paging (NP) is now supported. This feature reduces the complexity of memory management in virtualized environments. In addition, NP also reduces CPU utilization in memory-intensive guests.
At present, NP is not enabled by default. If your system supports NP, it is recommended that you enable NP by booting the hypervisor with the parameter hap=1.
This update to the Virtualization feature also includes the capability to install and run paravirtualized 32-bit guests on 64-bit hosts. However, this capability is provided as a Technology Preview; as such, it is not supported for production use.
- Shared Page Tables
Shared page tables are now supported for hugetlb memory. This enables page table entries to be shared among multiple processes.
Sharing page table entries among multiple processes consumes less cache space. This improves application cache hit ratio, resulting in better application performance.
- divider
The divider=<value> option is a kernel command-line parameter that allows you to adjust the system clock rate while maintaining the same visible HZ timing value to user space applications.
Using the divider= option allows you to reduce CPU overhead and increase efficiency at the cost of lowering the accuracy of timing operations and profiling. This is useful in virtualized environments as well as for certain applications.
Useful <values> for the standard 1000Hz clock are:
Note that the virtualized kernel uses a 250HZ clock by defaul. As such, it does not need the divider= option either in dom0 or in paravirtualized guests.
- Installing to dm-multipath Devices
Anaconda now has the capability to detect, create, and install to dm-multipath devices. To enable this feature, add the parameter mpath to the kernel boot line.
This feature was originally introduced in Red Hat Enterprise Linux 5 as a Technology Preview, and is now fully supported in this release.
Note that dm-multipath also features inbox support for the Dell MD3000. However, multiple nodes that use dm-multipath to access the MD3000 cannot perform immediate failback.
Further, it is recommended that you use the interface in Anaconda if your system has both multipath and non-multipath devices. Using in such cases may create both types of devices in the same logical volume groups.
At present, the following restrictions apply to this feature:
If there is only one path to the boot Logical Unit Number (LUN), Anaconda installs to the SCSI device even if mpath is specified. Even after you enable multiple paths to the boot LUN and recreate the initrd, the operating system will will boot from the SCSI device instead of the dm-multipath device.
However, if there are multiple paths to the boot LUN to begin with, Anaconda will correctly install to the corresponding dm-multipath device after mpath is specified in the kernel boot line.
By default, user_friendly_names is set to yes in multipath.conf. This is a required setting in the support implementation of the dm-multipath root device. As such, setting user_friendly_names to no and recreating the initrd will result in a boot failure with the following error:
Checking filesystems
fsck.ext3: No such file or directory while trying to open /dev/mapper/mpath0p1
- Booting from Storage Area Network (SAN)
The ability to boot from a SAN disk device is now supported. In this case, SAN refers to a Fibre Channel or iSCSI interface. This capability also features support for system-to-storage connection through multiple paths using dm-multipath.
In configurations that use multiple host bus adapters (HBA), you may need to set the system BIOS to boot from another adapter if all paths through the current adapter fail.
- Driver Update Program
The Driver Update Program (DUP) was designed to allow third-party vendors (such as OEMs) to add their own device drivers and other Linux Kernel Modules to Red Hat Enterprise Linux 5 systems using regular RPM packages as the distribution containers.
Red Hat Enterprise Linux 5.1 applies several updates to the DUP, most notably:
install-time Driver Update RPMs through Driver Update Disks is now supported
bootpath Driver Updates affecting the system bootpath are now supported
support for third-party packaging of Advanced Linux Sound Architecture (ALSA) is now deprecated
Further, various updates were applied to the approved kernel ABI symbol whitelists. These whitelists are used by packaging drivers to determine which symbols and data structures provided by the kernel can be used in a third-party driver.
Red Hat Summit