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Appendix B: Technology Background
Introduction to RAID
RAID (Redundant Array of Independent Disks) allows multiple hard drives to be
combined together to form one large logical drive or “array”. As far as the
operating system is concerned, the array represents a single storage device, and
treats it as such. The RAID software and/or controller handle all of the individual
drives on its own. The benefits of a RAID can include: higher data transfer rates
for increased server performance, increased overall storage capacity for a single
drive designation (such as, C, D, E, etc.), data redundancy/fault tolerance for
ensuring continuous system operation in the event of a hard drive failure.
Different types of arrays use different organizational models and have varying
benefits. The following outline breaks down the properties for each type of RAID
array:
RAID 0: Striping
When a disk array is striped, the read and write blocks of data are interleaved
between the sectors of multiple drives. Performance is increased, since the
workload is balanced between drives (or “members”) that form the array. Identical
drives are recommended for performance as well as data storage efficiency. The
disk array's data capacity is equal to the number of drive members multiplied by
the smallest array member’s capacity.
For example, one 100GB and three 120GB drives will form a 400GB (4 x 100GB)
disk array instead of 460 GB. The stripe block size value can be set logically from
4KB, 8KB, 16KB, 32KB, and 64KB. This selection will directly affect performance.
Larger block sizes are better for random disk access (like email, POS, or web
servers), while smaller sizes are better for sequential access.
1
3
5
7
2
4
6
8
Disk Drives
Data
Stripe
Figure 16. RAID 0 Striping Interleaves Data Across Multiple Drives
