Raid: redundant arrays of inexpensive disks INDEPENDENT

1. raid: redundant arrays of inexpensive disksINDEPENDENT Sean Traber CS-147 Fall 2009

2. Section 7.9 7.9 RAID 7.9.1 RAID Level 0 7.9.2 RAID Level 1 7.9.3 RAID Level 2 7.9.4 RAID Level 3 7.9.5 RAID Level 4 7.9.6 RAID Level 5 7.9.7 RAID Level 6 7.9.8 RAID DP (Double Parity) 7.9.9 Hybrid RAID Systems

3. Changing the acronym Originally stood for Redundant Arrays of Inexpensive Disks. The term �inexpensive� was too ambiguous and was assumed to be referring to cost which was not true. The term �inexpensive� was actually referring to the slight performance hit required to make the data storage reliable. The accepted acronym now uses �independent� instead of �inexpensive�.

4. The Authors Based on the 1988 paper �A Case for Redundant Arrays of Inexpensive Disks,� by David Patterson, Garth Gibson, and Randy Katz of U.C. Berkeley. They coined the term RAID and defined five types of RAID (called levels) These were the definitions of the levels numbered 1 through 5. Definitions for levels 0, 6, and DP came later. Many vendors offer enterprise-class storage systems that are not protected by RAID, these systems are often referred to as JBOD or Just a Bunch Of Disks.

5. 7.9.1 RAID Level 0 Not a true RAID implementation, lacks the �R� Very quick for Read/Write performance. Not a good way to store sensitive data. If one disk fails, all the data is lost. Less reliable than single disk systems. Array of 5 disks each with a design life of ~ 50,000 hours (6 years) gives the entire system an expected design life of 50,000/5 = 10,000 hours (14 months). As the number of disks increases, the probability of failure increases until it reaches near certainty.

6. RAID Level 0 Best used for data that is non-critical, or data that rarely changes and is backed up frequently.