Compaq, for example, only recommends and supports their drives. The recommended drives are sold under the Compaq name and helps Compaq guarantee a high level of quality and performance. But, this can be trouble if there is a problem with their supplier. Other RAID array vendors only use their drives, as is the case of the Micropolis disk array. But, this can lock you into one manufacturer.
Some systems allow for any drive to be used.
While this allows for greater drive selection it can also be a source of quality and performance problems if the wrong drive is chosen. Many RAID controllers are dual channel and will support at least 14 drives and some even more. Additionally, make sure multiple RAID controllers are supported in the same system. Make sure that a fast processor is used. It will save any unwritten data in cache in the event of a power failure.