Here is a good way to build a Raid5 Server
Hardware Requirement :
These 4 Drives will be in Raid5, so the available size will be 3xHDSize. ex: with 4x 1TB HD, available size will be 3TB
1 Install mdadm using apt-get, or your favorite package manager. mdadm is the tool used to administer Linux md device arrays (software RAID).
. Ensure that all partitions are of equal size and the partition type is set to Linux raid autodetect (code FD).
; subsituting for your own /dev/ devices.
4 Check if ok
5 Format your newly created /dev/md0 device in ext3.
6 Create a mount point for your RAID-5 array and add it to /etc/fstab so it is mounted automatically on the next reboot.
Removing a faulty disk from an array:
Clearing any previous raid info on a disk:
Adding a disk to an array:
HOWTO – Raid 5 Configuration