Chapter9.Bigger, Faster, More Reliable Storage with RAID

Chapter 9. Bigger, Faster, More Reliable Storage with RAID

Upon completing this chapter, you will be able to

• Participate in discussions and planning sessions regarding the use of RAID technology in storage network designs

• Compare the advantages and disadvantages of parity RAID and mirroring

• Describe the exclusive OR (XOR) operation used in parity RAID, and describe the processes of degraded mode operations and parity rebuilds

• Discuss the difference between RAID 10 and RAID 5, including the RAID 5 write penalty

RAID (redundant array of inexpensive disks) is one of the most important technologies in storage networking and is one of the main functions of storage virtualization. While many people associate RAID with hardware products, such as disk subsystems and RAID adapters, RAID is actually a set of software algorithms that aggregate storage input/output (I/O) operations across multiple storage address spaces. RAID is usually applied with disk drives in disk subsystems, but it can also be applied across multiple disk subsystems in a storage network. In fact, RAID algorithms can be applied across any combination of storage address spaces, whether they are storage devices, logical unit numbers (LUNs) exported by subsystems, or logical volumes created by host volume management software.

NOTE

The "I" in RAID stands for inexpensive, although it is often referred to as "independent." Both work, but historically, inexpensive is correct. The "D" in RAID stands for disks, but that should not be taken too literally. The RAID algorithms are independent of the type of storing technology used, as long as they have the same storage capacity.