Adaptec 3405 User Guide - Page 83

Understanding Drive Segments, Non-redundant Arrays (RAID 0), drive segment, RAID segments, striping

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Appendix B: Understanding RAID ● 83 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 1 250 GB Drive Segment Size (Smallest Disk Drive) Disk Drive 2 250 GB Disk Drive 3 400 GB Disk Drive 4 400 GB Disk Drives in Logical Drive Disk Drive 1 1 5 ... 997 Disk Drive 2 2 6 ... 998 Disk Drive 3 3 7 ... 999 Unused Space = 150 GB Disk Drive 4 4 8 ... 1000 Unused Space = 150 GB RAID 0 Logical Drive = 1000 GB

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Appendix B: Understanding RAID
●
83
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
perfor
mance.
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
250 GB
250 GB
400 GB
400 GB
Drive Segment Size
(Smallest Disk Drive)
Disk Drive 2
Disk Drive 3
Disk Drive 4
Disk Drive 1
1
5
...
997
2
6
...
998
3
7
...
999
4
8
... 1000
Unused Space = 150 GB
Disk Drives in Logical Drive
RAID 0 Logical Drive = 1000 GB
Unused Space = 150 GB