I don't really have an answer for you, 'cause I haven't personally used RAID in like a decade. I did a very quick search to see if it was possible to deal with RAID after installing the OS and came away with this link:
I haven't setup software raid in a long time but if you want it setup on the os disk(s) you will have to do it during the installation process. With CentOS there is an option for it at the disk setup window where you also create partitions.
I just did the setup I think you want in a vm, I think you are looking for something like this.
Code:
[root@localhost ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sr0 11:0 1 1024M 0 rom
vda 253:0 0 20G 0 disk
├─vda1 253:1 0 18G 0 part
│ └─md125 9:125 0 18G 0 raid1 /
├─vda2 253:2 0 1G 0 part
│ └─md127 9:127 0 1G 0 raid1 [SWAP]
└─vda3 253:3 0 1G 0 part
└─md126 9:126 0 1022M 0 raid1 /boot
vdb 253:16 0 20G 0 disk
├─vdb1 253:17 0 18G 0 part
│ └─md125 9:125 0 18G 0 raid1 /
├─vdb2 253:18 0 1G 0 part
│ └─md127 9:127 0 1G 0 raid1 [SWAP]
└─vdb3 253:19 0 1G 0 part
└─md126 9:126 0 1022M 0 raid1 /boot
That's the best the installer can do which is first you create your partitions and volumes and then you can select which volumes you want to be raid and which raid version you want them to be. If you want a different raid setup where the whole disk is a raid device you will have to do boot from a live cd and then do your custom raid setup through the command-line. After which you can boot the centos installer and install the system on your custom raid setup.
