APPENDIX A - 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 handles 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 (see Figure A1). 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 1GB and three 1.2GB drives will form a 4GB (4 x 1GB) disk array instead of 4.6 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.
RAID 0 (Striping)
Figure A1. RAID 0 striping interleaves data across multiple drives
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