The A+ Exams Guide: (Exam 220-301), (Exam 220-302) (TestTakers Guides)

Although the A+ Core exam is not likely to nail you with high-level questions regarding the various types of RAID (Redundant Array of Independent Disks) implementations, it is important for you to understand the basic implementations of RAID. Besides, anyone pursuing a career in the computing industry needs to understand fault-tolerance basics and RAID.

RAID is one of the most popular means of providing fault-tolerant systems in use today. Through a process known as disk or 'data' striping, RAID divides data into separate units and distributes the data across two or more hard disks. There are many variations of RAID available; the most popular are:

• RAID level 0. This level of RAID is not considered fault tolerant. It spreads data in blocks across multiple disks, but provides no data redundancy. This level of RAID only produces better performance. If one disk fails with this configuration, all data is lost.

• RAID level 1. This level is also known as 'disk mirroring.' With RAID level 1, all data is duplicated or ‘written to' a second hard disk. If one of the disks fails, the information is still available on the second disk. This level of RAID is fault tolerant, although its performance is not rated as well as RAID level 5.

• RAID level 3. This level also spreads data units across several disks, but it also uses a dedicated disk for parity information, which is used for error-correction purposes. In simple terms, it provides a basic level of fault tolerance.

• RAID level 5. Level 5 provides excellent fault tolerance and good performance. It stores parity information across all disks in the disk array and provides concurrent disk reads and writes. It is the most popular RAID implementation.

With all that being said about RAID, it is important that you know that RAID requires fast controllers/interfaces to be effective. All that reading and writing to multiple hard disks can quickly hamper a workstation's or server's ability to properly store and process data.