Then I tried with Centos 6 and faced the same problem, no harddisk detected. Fortunately, I found some info in a forum mention about one need to configure the harddisk in the BIOS first. Aha. This is actually where the issue exist.
In order to configure the harddisks in the BIOS, just boot up the server and wait until a screen mention about Megaraid WebBIOS Configuration, press Ctrl-H.
Then, configure the harddisks as Array RAID. After that, just use Configuration Wizard to set them as as many Disk Group as needed. At this point, Centos 6 could detect the harddisk.
Find official guide from IBM, Installation and User's Guide - IBM ServeRAID-M Software (WebBIOS, MegaRAID Storage Manager, and MegaCLI), here.