Raid 1 Arrays; Raid 1 Enhanced Arrays - Adaptec ASR-6805Q User Manual

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 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 figure.
250 GB
Disk Drive 1
Disk Drive 2 400 GB
Disk Drives in Logical Drive

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 1
400 GB
Disk Drive 2 400 GB
Disk Drive 3 400 GB
Disk Drives in Logical Drive
Proprietary and Confidential to PMC-Sierra, Inc.
Document No.: CDP-00277-02-A Rev. A, Issue:
Serial Attached SCSI RAID Controllers Installation and User's Guide
Drive Segment Size
(Smallest Disk Drive)
Disk Drive 1 1 – 250
Disk Drive 2 1 – 250
RAID 1 Logical Drive = 250 GB
Disk Drive 1
3
Disk Drive 2
1
Disk Drive 3
2
RAID 1E Logical Drive = 600 GB
Unused Space = 150 GB
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4
5
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