Appendix B: Understanding RAID
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Understanding Drive Segments
A drive segment is a disk drive or portion of a disk drive that is used to
create an array. A disk drive can include both RAID segments (segments
that are part of an array) and available segments. Each segment can be
part of only one logical device at a time. If a disk drive is not part of any
logical device, the entire disk is an available segment.
RAID 0 (Non-RAID Arrays)
An array with RAID 0 includes two or more disk drives (maximum
twelve) and provides data striping, where data is distributed evenly
across the disk drives in equal-sized sections.
RAID 0 arrays do not maintain redundant data, so they offer no data
protection. However, compared to an equal-sized group of independent
disks, a RAID 0 array provides improved I/O performance.
Drive segment size is limited to the size of the smallest disk drive in the
array. For instance, an array with two 250 GB disk drives and two 400
GB disk drives can create a RAID 0 drive segment of 250 GB, for a total
of 1000 GB for the volume, as shown below.
Disk Drive 1
Disk Drive 2
Disk Drive 3
Disk Drive 4
250 GB
250 GB
400 GB
400 GB
Disk Drives in Logical Drive
Disk Drive 1
Disk Drive 2
Disk Drive 3
Disk Drive 4
RAID 0 Logical Drive = 1000 GB
1
2
3
4
Not Used
Not Used
5
6
7
8
1000
999
998
997
...
...
...
...
Unused Space: 150 GB
Unused Space: 150 GB
Drive Segment Size (Smallest Disk Drive)
