Linked from: Configuring Partitions and RAID
For software RAID 5, you need at least three hard disks. Since the RAID partitions on both the hard disks must be of equal size, it is a good idea to use hard disks with (roughly) the same storage capacity.
In our example, we are using three SATA disks. These hard disks are detected in Linux as:
For purposes of this demonstration we will assume that /dev/sda is used for the system RAID partition, swap, and boot partition.
Please refer to Deleting Partitions if you need assistance in removing existing partitions.
We will create a large RAID 5 volume for our file server using /var/flexshare/shares as our mount point. This will allow our file server to optimize for space.
Repeat the same process for sdc and sdd, be sure to mark the correct allowable drive and take the marks off of all the other drives.
Now that we should have three identical configurations, we can create the software RAID disk:
Once completed, click OK and continue through the boot loader installation process. Please refer to Boot Loader document for if you require help with this step.