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Appendix B: Technology Background
XX102-00-00 Rev 203 KOL-RAID3 RAID Storage Systemd
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.
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Data
Stripe
Figure 15. RAID 0 Striping Interleaves Data Across Multiple Drives
RAID 1: Mirroring
When a disk array is mirrored, identical data is written to a pair of drives, while reads are performed in parallel. The reads
are performed using elevator seek and load balancing techniques where the workload is distributed in the most efficient
manner. Whichever drive is not busy and is positioned closer to the data will be accessed first.
With RAID 1, if one drive fails or has errors, the other mirrored drive continues to function. This is called Fault Tolerance.
Moreover, if a spare drive is present, the spare drive will be used as the replacement drive and data will begin to be
mirrored to it from the remaining good drive.
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Data Mirror
Figure 16. RAID 1 Mirrors Identical Data to Two Drives