High availability is when servers are kept online as much as possible. The average amount of money lost for internet companies when their websites go offline is $1,000,000 per hour! It might seem good if a server is up 99.9% of the time but that 0.1% of the year could cost a company $8,760,000.

What is RAID?

Background:
     RAID stands for Redundant Array of Inexpensive or Independent Disks. RAID provides crash-proof hard drive systems. RAID can provide increased speed as well as redundancy.

RAID Levels:
     Six distinctive RAID levels have been developed and agreed upon, by various manufacturers. These RAID levels are 0, 1, 2, 3, 4, and 5. A RAID system appears as a single large hard disk to the operating system.

Why do servers use RAID?
     RAID provides more effecient storage solutions than using single drives. RAID level 1 provides a real time backup of important data so if a drive is lost the data is safe. RAID levels 3 and 5 provide redundancy with as well as speed.

High availability and all levels of RAID are covered in Server+.