RAID Technology Overview - September 2007

Figure 2-2 Disk Drive Mirroring of P1 onto P2 (RAID 1)
The advantages of RAID 1 are as follows:
• No data loss or interruption of service if a disk fails.
• Fast read performance — data is available from either disk.
The disadvantages of RAID 1 are as follows:
• High cost — 50% of disk space is allocated for data protection, so only 50% of total disk
drive capacity is usable for data storage.
RAID 1+0: Disk Mirroring and Striping
RAID 1+0 requires an array with four or more physical disks. The disks are mirrored in pairs
and data blocks are striped across the mirrored pairs.
Figure 2-3 Mirroring and Striping (RAID 1+0)
In each mirrored pair, the physical disk that is not busy answering other requests answers any
read request sent to the array; this behavior is called load balancing. If a physical disk fails, the
remaining disk in the mirrored pair can still provide all the necessary data. Several disks in the
array can fail without incurring data loss, as long as no two failed disks belong to the same
mirrored pair.
This fault-tolerance method is useful when high performance and data protection are more
important than the cost of physical disks.
16 Smart Array Controller Supported RAID Configurations