Redundant Array of Inexpensive Disks (RAID) is a group of strategies designed to provide fault tolerance for files stored on hard drives . In general, using RAID means that you are placing data on more than one disk; if a disk in the RAID set goes down, you still can get to your data because you either have a complete copy of that data (on another disk in the RAID set) or can regenerate the data on the failed disk from the data and parity information (something we will discuss when we look at RAID 5) on the remaining disks in the set.
In the simplest terms, RAID allows you to take more than one drive and combine them into a disk set (or array ) that functions just like a single drive. RAID can be hardware supported or software supported. Hardware RAID will be available on a computer where the SCSI controllers found on the motherboard support RAID. Some sort of configuration utility will be provided to set up RAID on a computer that supports hardware RAID. You can also buy add-on boards such as a SCSI controller card.
With software RAID, the operating system you are running (and this is pretty much limited to network operating systems and Windows 2000 and XP Professional clients ) supports RAID. Windows 2000 and Windows Server 2003, Novell NetWare, some Linux distributions, Sun Solaris, and other network operating systems provide support for software RAID.