Raid
Raid
RAID is an acronym for Redundant Array of Indexed Disks. It uses multiple hard disks storing the same data to protect against some degree of physical disk failure. The amount of protection it affords depends upon the type of raid used.
Software Raid
The supported, and probably optimal, way to use raid with Ubuntu is to employ Linux's Multiple Device (md) raid system, optionally with the Logical Volume Manager (LVM).
Installation
In Breezy Badger (5.10), installation of md and LVM can be completed entirely with the installation CD without using expert mode.
Just md
This is the simplest method of setting up software raid. It uses one raid partition per operating system partition, unlike LVM which uses logical volumes in order to use a single raid partition. For each disk in the array create a "Use as: Raid physical" partition of appropriate size for each operating system partition (/boot, /, swap, /home, etc.). The /boot or / partitions on each disk should be marked bootable. Use configure raid to make raid devices for each partition. On each of these raid devices configure a single operating system partition (/boot, /, swap, etc.) of the size of the entire device. Continue installing Ubuntu.
* http://www.howtoforge.com/linux_software_raid More detailed instructions for Debian and Ubuntu
Other Setups
* ["Installation/LVMOnRaid"] Setup using both LVM and md. The LVM setup didn't work for me. * ["Installation/RAID1"] an older description for Warty Warthog.
FakeRaid
Most, in not all, of the so called "raid controllers" installed on motherboards are actually just hard drive controllers with a few extra features to make it easy to implement software raid drivers. These are highly non-standard. Each chipset uses different on-disk formats and different drivers. These systems are not extremely desirable for use with Ubuntu; the completely software raid described above is better. They are primarily of interest when compatibility with another existing system that employs them is required.
Access
Device mapper raid can be used to access many of these volumes. It is provided by the dmraid package. dmraid is in the Universe repository.
After installing dmraid you can run the command <code>dmraid -r</code> to list the devices and raid volumes on your system. dmraid makes a device file for each volume and partition; these can be found in the /dev/mapper/ directory, and can be mounted and otherwise manipulated like normal block devices. Other options of the dmraid program are used to administer the array.
Installation
It is not advisable to install Ubuntu onto disks managed by a fake raid system; it is extremely difficult and the results will be disappointing compared to Linux's LVM and md software raid system. If you really must do it to install Ubuntu on the same raid array as an existing installation of another operating system see the following:
More Information
Mixing Software Raid
Ubuntu can be installed on its own raid array on a computer that is using FakeRaid for another operating system on another array. There are a few steps that need to be followed for this to work:
Identify which drives are the existing operating system. You can do this by booting the Ubuntu Live CD, enabling the universe repository, installing dmraid, mounting the partitions, and poking around. You can see which devices were which mapped block device by running <code>dmraid -r</code>.
- Disable the fake raid support in the bios for the drives that Ubuntu will be installed onto.
- Install Ubuntu onto those drives by partitioning them each with a single, full-sized "raid" type partition, setting up LVM groups, and adding at least root (/) and swap partitions inside.
Hardware Raid
Real hardware raid systems are very rare, and are almost always provided by a card such as a PCI card. Your hardware will need kernel level support in order to work with Ubuntu. You can find out if is is supported without much work by booting a Live CD. Your array should be visible as a scsi block device and, if it has existing partitions and file systems, mountable.
Links
http://www.linuxmafia.com/faq/Hardware/sata.html Information about SATA controllers, including fakeraid.