Installation guide

dmraid
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mdraid also supports other metadata formats, known as external metadata. Red Hat Enterprise Linux
6 uses mdraid with external metadata to access ISW / IMSM (Intel firmware RAID) sets. mdraid sets
are configured and controlled through the mdadm utility.
dmraid
Device-mapper RAID or dmraid refers to device-mapper kernel code that offers the mechanism to
piece disks together into a RAID set. This same kernel code does not provide any RAID configuration
mechanism.
dmraid is configured entirely in user-space, making it easy to support various on-disk metadata
formats. As such, dmraid is used on a wide variety of firmware RAID implementations. dmraid
also supports Intel firmware RAID, although Red Hat Enterprise Linux 6 uses mdraid to access Intel
firmware RAID sets.
13.6. RAID Support in the Installer
The Anaconda installer will automatically detect any hardware and firmware RAID sets on a system,
making them available for installation. Anaconda also supports software RAID using mdraid, and
can recognize existing mdraid sets.
Anaconda provides utilities for creating RAID sets during installation; however, these utilities only
allow partitions (as opposed to entire disks) to be members of new sets. To use an entire disk for a set,
simply create a partition on it spanning the entire disk, and use that partition as the RAID set member.
When the root file system uses a RAID set, Anaconda will add special kernel command-line options to
the bootloader configuration telling the initrd which RAID set(s) to activate before searching for the
root file system.
For instructions on configuring RAID during installation, refer to the Red Hat Enterprise Linux 6
Installation Guide.
13.7. Configuring RAID Sets
Most RAID sets are configured during creation, typically through the firmware menu or from the
installer. In some cases, you may need to create or modify RAID sets after installing the system,
preferably without having to reboot the machine and enter the firmware menu to do so.
Some hardware RAID controllers allow you to configure RAID sets on-the-fly or even define
completely new sets after adding extra disks. This requires the use of driver-specific utilities, as
there is no standard API for this. Refer to your hardware RAID controller's driver documentation for
information on this.
mdadm
The mdadm command-line tool is used to manage software RAID in Linux, i.e. mdraid. For
information on the different mdadm modes and options, refer to man mdadm. The man page also
contains useful examples for common operations like creating, monitoring, and assembling software
RAID arrays.
dmraid
As the name suggests, dmraid is used to manage device-mapper RAID sets. The dmraid tool finds
ATARAID devices using multiple metadata format handlers, each supporting various formats. For a
complete list of supported formats, run dmraid -l.