Microsemi Adaptec ASR-8405E - RAID 1 Arrays; RAID 1 Enhanced Arrays

B.3 RAID 1 Arrays
A RAID 1 array is built from two disk drives, where one disk drive is a mirror of the other (the same data is
stored on each disk drive). Compared to independent disk drives, RAID 1 arrays provide improved
performance, with up to twice the read rate and an equal write rate of single disks. However, capacity is
only 50 percent of independent disk drives.
If the RAID 1 array is built from different- sized disk drives, the free space, drive segment size is the size of
the smaller disk drive, as shown in this gure.
Disk Drive 2
Disk Drive 1
400 GB
Drive Segment Size
(Smallest Disk Drive)
Disk Drive 1
Disk Drive 2
Disk Drives in Logical Drive
RAID 1 Logical Drive = 250 GB
1 – 250
1 – 250
Unused Space = 150 GB
250 GB
B.4 RAID 1 Enhanced Arrays
A RAID 1 Enhanced (RAID 1E) array—also known as a striped mirror—is similar to a RAID 1 array except that
data is both mirrored and striped, and more disk drives can be included. A RAID 1E array can be built from
three or more disk drives.
In this example, the large bold numbers represent the striped data, and the smaller, non-bold numbers
represent the mirrored data stripes.
Disk Drive 2 400 GB
400 GB
400 GBDisk Drive 3
Disk Drive 2
Disk Drive 1
Disk Drive 3
3
1
2
6
4
5
Disk Drives in Logical Drive RAID 1E Logical Drive = 600 GB
Disk Drive 1
50
Microsemi Proprietary and Condential. Installation and User's Guide Revision 5
Understanding RAID