Adaptec 48300, 58300, 44300, 1220SA RAID 1 Arrays, RAID 10 Arrays, Disk Drives in Logical Drive

Appendix B: Understanding RAID ● 66

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 the following figure.

Disk Drive 1	Drive Segment Size (Smallest Disk Drive)
	250 GB
Disk Drive 2
	250 GB
		Disk Drive 1	1	5 ...	997
Disk Drive 3		Disk Drive 2	2		998
				6 ...
	400 GB
		Disk Drive 3	3	7 ...	999
					Unused Space: 150 GB
				Not Used
Disk Drive 4	400 GB	Disk Drive 4 4		8 ...	1000
					Unused Space: 150 GB
				Not Used
Disk Drives in Logical Drive		RAID 0 Logical Drive = 1000 GB

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 the following figure.

		Drive Segment Size (Smaller Disk Drive)
Disk Drive 1	250 GB
		Disk Drive 1	1 – 250
Disk Drive 2	400 GB	Disk Drive 2	1 – 250

Unused Space: 150 GB

Not Used

Disk Drives in Logical Drive RAID 1 Logical Drive = 250 GB

RAID 10 Arrays

A RAID 10 array is built from two or more equal-sized RAID 1 arrays. Adaptec RAID controllers support a maximum number of 48 disk drives in a RAID 10 array.

Data in a RAID 10 array is both striped and mirrored. Mirroring provides data protection, and striping improves performance.