Controller-Based Replication As the name implies, the storage system controller performs the replication process. The controller keeps track of what drives (or pieces of drives) are being replicated and simply sends that information to those drives whenever necessary. Note the distinction that this is not a form of RAID. While hardware RAID is typically performed at the controller level, it is typically performed through a combination of hardware and software components specifically designed for RAID. Every storage vendor implements RAID in their own way, and this is not within the scope of this tutorial. Since controller-based replication resides on the controller, it requires either a different set of or additional firmware to be loaded on the controller than the standard version of microcode. This is not a big concern, except for the normal problems that occur when licenses are involved.