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RAID Overview
RAID is a collection of specifications that describe a system for ensuring the reliability
and stability of data stored on large disk subsystems. A RAID system can be implemented
in a number of different versions (or RAID levels). The standard RAID levels are 0, 1, 3,
and 5. This controller supports RAID levels 0, 1, and 10 (spanned RAID 1 arrays).
Disk Striping
Disk striping writes data across multiple hard drives instead of just one hard drive. Disk
striping involves partitioning each drive storage space into stripes that can vary in size.
These stripes are interleaved in a repeated sequential manner. The combined storage
space is composed of stripes from each drive. IBM IDE supports stripe sizes of 32 KB to
4 MB.
For example, in a four-disk system using only disk striping (as in RAID level 0), segment
1 is written to disk 1, segment 2 is written to disk 2, and so on. Disk striping enhances
performance because multiple drives are accessed simultaneously; but does not provide
data redundancy.
Figure 2-1. Disk Striping
Segment 1
Segment 3
Segment 5
Segment 7
Stripe Width
Stripe width is the number of disks involved in an array where striping is implemented.
For example, a four-disk array with disk striping has a stripe width of four.
Stripe Size
The stripe size is the length of the interleaved data segments that are written across
multiple drives.
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IBM ATA 133 RAID Controller User's Guide
Data Flow
Segment 2
Segment 4
Segment 6
Segment 8
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