This is basically a controller card disk which is capable of supporting one or more configurations. It was originally meant only for the SCSI drives, but the RAID Controllers just became really popular for both the SATA and PATA drives

What are RAID Controllers

It is technically a device that manages the physical disk drives, and then thereby presents them to the computer in such a form as of logical units. Yet in most cases, implements hardware, thus it is sometimes referred to as RAID controller. It also often useful in that it provides the additional disk cache. The  controller is capable of offering a level of notion between the operating system as well as the physical computer drives. The RAID controller provides groups of the various applications and the operating systems, as logical units for which the data protection schemes can then be defined. Since the controller is capable of accessing multiple copies of various data on multiple devices, it is therefore capable of improving performance and can protect data in the event that a system crash occurs.

In the Hardware-Based RAID, physical controllers is used in managing the RAID arrangement. The controller can also take various forms such as a PCI or PCI Express card that is designed to support only a specific drive format like SATA. However, some of the RAID controllers could also be integrated with motherboards. The controller may also be software-purely, thereby using the hardware resources belonging to the host system. The Software-based RAID generally gives similar functionality as to that which is hardware-based RAID, but typically less in performance than of the hardware versions.

RAID Controller Failure Causes and Remedies

RAID controller failures may occur due to a variety of reasons. Normally a technician would assume that one of the drives has failed.  It is a very common diagnosis for RAID controller failures as the diagnostic lights on the drives may be blinking, gone orange, or as may be in some cases the drive may not be spinning.  These surface indicators would definitely lead the technician to assume that the drives have either failed or are on their way out.  There is, however, another reason why all these things might occur, and that would definitely be a RAID controller failure.  The challenge is to be able to diagnose the problem with a damaged controller.

However, despite the advantages offered by the RAID arrays, there are certain disadvantages as well, e.g. should the RAID controller fail, it will become very hard or even in some cases not possible to continue making use of the RAID array in the original arrangement. In various cases, the user data and files end up becoming inaccessible with no original or a well-suited RAID controller required.

In the event that your RAID controller does fail and you need access to your data, you need to consider making use of a dedicated RAID recovery device to be able to recover data and files from the inaccessible array and putting all the recovered files onto one hard disk.