Here's some notes.
To use RAID, you need to have two or more drives partitioned as Linux RAID members and you need to note down which of these devices will become members of your array. This guide will not cover how to partition drives suffice to say that you can do it using fdisk (console) or gparted (gui). Remember, as always, Google is your friend!
The first step (after partitioning your target drives) is to install the Linux raid utils package.
sudo apt-get install mdadm
This is the command I use to create a 4 drive RAID0 (stripe, no parity) array
sudo mdadm --create /dev/md0 --level=0 --raid-devices=4 /dev/sdd /dev/sde /dev/sdf /dev/sdg
Simply change the "level" to make a RAID5 (stripe with parity) array
sudo mdadm --create /dev/md0 --level=5 --raid-devices=4 /dev/sdd /dev/sde /dev/sdf /dev/sdg
To add another drive later on use this command;
sudo mdadm /dev/md0 --add /dev/sdh
It seems that every time I have to rebuild a system with a pre-existing array I have trouble with it automagically mounting an array called /dev/md_d0 at reboot and everything gets borked until you manually fix it. This is what I have to do;
Logon as su (you need to do this in order to run the mkconf)
Stop the automagic array
mdadm --manage /dev/md_d0 --stop
Re-create the array properly
mdadm --create /dev/md0 --level=0 --raid-devices=4 /dev/sdd /dev/sde /dev/sdf /dev/sdg
Recreate the mdadm config for the array
/usr/share/mdadm/mkconf > /etc/mdadm/mdadm.conf
I prefer to use UUID rather than discrete devices whenever possible;
Find the UUID of the array.
This will return something like this;
/dev/md0: UUID="895c982b-5d2c-4909-b5bf-4ba5a1d049e9" TYPE="ext3"
Add a line to automatically mount the array in /etc/fstab
Here is a typical line
UUID=895c982b-5d2c-4909-b5bf-4ba5a1d049e9 /store ext3 defaults,relatime,errors=remount-ro 0 2
You need to change the the UUID to the one that was returned by the above blkid command as well as the mount point that you want to mount it on. Make sure you create the appropriate mount point too!
Once this is all done you should be up and running.
To permanently remove raid member disks;
sudo mdadm --zero-superblock /dev/sdX
Good luck and have fun with the penguin!
(last revised 12/08/2010)