Adaptec 44300 User Guide - Page 65

Appendix B: Understanding RAID ● 65 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 1 250 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 2 998 6 ... Disk Drive 3 3 999 7 ... Not Used Unused Space: 150 GB Disk Drive 4 4 8 ... 1000 Not Used Unused Space: 150 GB 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. Disk Drive 1 250 GB Drive Segment Size (Smaller Disk Drive) Disk Drive 1 1 - 250 Disk Drive 2 400 GB Disk Drives in Logical Drive Disk Drive 2 1 - 250 Not Used Unused Space: 150 GB 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.