RAID!?!

RAID!?!

Time Shaver Though not specifically listed in the blueprint of the Core Hardware exam, you should have some understanding of RAID technology in case it's included in a situational question or as an answer option.

A Redundant Array of Independent Disks (RAID) is a storage technology that uses two or more hard drives in combination for high availability, fault tolerance (error recovery), and performance. RAID disk drives are used frequently on servers but generally aren't necessary for a personal computer.

One of the fundamental concepts of RAID drives is data striping. In this process, data files are subdivided and written to several disks. This technique allows the processor to read or write data faster than a single disk can supply or accept it. While the first data segment transfers from the first disk, the second disk is locating the next segment, and so on.

Another common feature of RAID systems is data mirroring. This feature involves writing duplicate data segments or files to more than one disk to guard against losing the data should a hard drive fail.

Ten different RAID levels exist--0 through 7, 10, and 53, each more complicated than its predecessor.

The RAID levels are:

l RAID 0 -- Data Striping: Interleaves data across multiple drives. Doesn't include mirroring, redundancy or any other protection against device failure. RAID 0 is not fault tolerant.

l RAID 1--Data Mirroring: Provides fault tolerance by completely duplicating data on two independent drives. This provides a failover disk in the event that one of the mirrored disks should fail.

l RAID 3--Parallel Transfer with Parity: Provides fault tolerance by transferring data to and from three or more hard drives with data striped across the drives and the parity bits, which are used to reconstruct the data in the event of a drive failure and stored on a separate and dedicated drive.

l RAID 5--Data Striping with Parity: Provides fault tolerance by employing essentially the same application as RAID 3. However, RAID 5 stores the parity bits from two drives on a third drive to provide for data stripe error correction. This is the most popular RAID technology implemented.