Appendix B Understanding Raid; Understanding Drive Segments; Non-Redundant Arrays (Raid 0) - Adaptec CDP-00277-01-A Installation And User Manual

B Understanding RAID
When you create arrays (or logical drives), you can assign a RAID level to protect your data.
Each RAID level offers a unique combination of performance and redundancy. RAID levels also vary by
the number of disk drives they support.
This appendix describes the RAID levels supported by your Adaptec RAID controller, and provides a basic
overview of each to help you select the best level of protection for your data storage.

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.

Non-redundant Arrays (RAID 0)

An array with RAID 0 includes two or more disk drives and provides data striping, where data is distributed
evenly across the disk drives in equal-sized sections. However, RAID 0 arrays do not maintain redundant
data, so they offer no data protection.
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 in this figure.
Disk Drive 1
Disk Drive 2
Disk Drive 3
Disk Drive 4
Disk Drives in Logical Drive
Proprietary and Confidential to PMC-Sierra, Inc.
Document No.: CDP-00277-01-A Rev. A, Issue:
Drive Segment Size
250 GB
(Smallest Disk Drive)
250 GB
Disk Drive 1
Disk Drive 2
400 GB
Disk Drive 3
Disk Drive 4
400 GB
Serial Attached SCSI RAID Controllers Installation and User's Guide
1 5 . . . 997
2 6 . . . 998
3 7 . . . 999
4 8 . . . 1000
RAID 0 Logical Drive = 1000 GB
Unused Space = 150 GB
Unused Space = 150 GB
64