Promise Technology 66 Pro - Manual (Page 125)

SuperTrak66™ User's Manual Appendix A
A-1
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 RAID can include: higher data transfer rates for increased
server performance, increased overall storage capacity for a single drive designation
(i.e. 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 next page). 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 1KB, 2KB,
4KB, 8KB, 16KB, 32KB, 64KB [Default], 128KB, 256KB, 512KB, or 1024KB. 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. NOTE: Promise recommends to use a block size smaller than
64KB for video-editing applications.