FakeRaidHowto

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#format wiki
#language en
== How to configure ubuntu to access a hardware fakeraid ==

This is my first time editing a wiki, so bear with me. This page is a work in progress. I have spent the last week getting ubuntu breezy preview installed on my via sata fakeraid and finally have the system dual booting winxp and ubuntu linux on a raid-0 ( stripe ) between two 36 gig 10,000 rpm WD raptor hard drives. I thought I would create a howto to describe how I did it so that others may benefit from my work.

=== What is it? ===
In the last year or two a number of hardware products have come on the market claiming to be IDE or SATA raid controllers. Virtually all of them are not really hardware raid controllers. Instead they are simply a multi channel disk controller that has special bios and drivers for the OS to perform the software raid functions. This has the effect of giving the appearence of a hardware raid, because the raid configuration is set up using a bios setup screen and the system can be booted from the raid.

Under windows, you must supply a driver floppy to the setup process so windows can access the raid. Under linux, the hardware is seen for what it is, which is simply a multi channel IDE/SATA controller. What this means is that if you have multiple disks configured as a raid, linux sees individual disks. This page describes how to get linux to see the raid as one disk, and boot from it. In my case, I use a raid-0 configuration, but this should also apply to raid-1 and raid-5.

=== Background ===
In recent years there has been a trend to try and pull a bunch of code out of the kernel and into early user space. This includes stuff like nfsroot configuration, md software raid, lvm, conventional partition/disklabel support, and so on. Early user space is set up in the form of an initramfs which the boot loader loads with the kernel, and this contains user mode utilities to detect and configure the hardware, mount the correct root device, and boot the rest of the system.

Hardware fakeraid falls into this category of operation. A device driver in the kernel called device mapper is configured by user mode utilities to access software raids and partitions. If you want to be able to use a fakeraid for your root filesystem, your initramfs must be configured to detect the fakeraid and configure the kernel mapper to access it.
#REFRESH 0 http://help.ubuntu.com/community/FakeRaidHowto

FakeRaidHowto (last edited 2008-08-06 17:00:01 by localhost)