RAID: software VS hardware
You didn't wrote which kind of RAID you are using. There's two main categories:
Hardware RAID: the RAID stuff is managed by your hard drive controller and the devices shown in your Linux are an abstract of your array. Usually, there's a firmware accessible during the boot to configure the array (RAID 0, 1, etc...). The devices may be named
/dev/sdX or something else more exotic like, for example with HP SmartArray controller,
Software RAID: the RAID stuff is totally managed by your operating system. You have, to setup the array on operating system side, usually during the install process or later using
mdadm. Usually, software RAID create devices under
/dev/mdXX. Your single drives are still visible under
/dev/sdX but must not be accessed directly.
Formatting under Linux
The command you typed (
dd if=/dev/zero [...]) has nothing to deal with formatting.
With these commands, you simply zero-ed your disks which is totally useless unless you want to remove any vestige of the data previously stored on it.
To format, you must use of one the
XXXX is the filesystem you want to use. For example
/sbin/mkfs.ext4 /dev/sda1 will format partition 1 of the first drive with Ext4 filesystem.