Adaptec 6805Q 2270700-R User Manual
Product codes
2270700-R
Appendix B: Understanding RAID
●
97
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.
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.
the size of the smaller disk drive, as shown in this figure.
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.
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.
numbers represent the mirrored data stripes.
Disk Drive 2
Disk Drive 1
250 GB
400 GB
Drive Segment Size
(Smallest Disk Drive)
(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
Disk Drive 2
Disk Drive 1
400 GB
Disk Drives in Logical Drive
RAID 1E Logical Drive = 600 GB
400 GB
400 GB
Disk Drive 3
Disk Drive 2
Disk Drive 1
Disk Drive 3
1
3
2
3
4
5
6
1
2
6
4
5