The need for RAID can be summarized in two points given below. The two
keywords are Redundant and Array.
With a single hard disk, you cannot protect yourself against the costs of a disk failure, the time required to obtain and install a replacement disk, reinstall the operating system, restore files from backup tapes, and repeat all the data entry performed since the last backup was made.
With multiple disks and a suitable redundancy scheme, your system can
stay up and running when a disk fails, and even while the replacement disk
is being installed and its data restored.
To create an optimal cost-effective RAID
we need to simultaneously achieve the following goals: