RAID Technology Overview - September 2007

2 Smart Array Controller Supported RAID Configurations
This chapter provides details about each of the RAID levels that are supported by HP Smart
Array Controllers. This chapter addresses the following topics:
“RAID 0: No Fault Tolerance”
“RAID 1: Disk Mirroring” (page 15)
“RAID 1+0: Disk Mirroring and Striping” (page 16)
“RAID 5: Distributed Data Guarding” (page 17)
“RAID ADG: Advanced Data Guarding” (page 17)
“Summary of RAID Methods” (page 19)
“Choosing a RAID Method” (page 19)
RAID 0: No Fault Tolerance
The RAID 0 configuration enhances performance with data striping, but there is no data
redundancy to protect against data loss when a physical disk fails. RAID 0 is useful for rapid
storage of large amounts of non-critical data (for printing or image editing, for example), or when
cost is the most important consideration (see Figure 2-1 (page 15)).
Figure 2-1 Data Striping (S1-S4) of Data Blocks B1-B12
The advantages of RAID 0 are as follows:
• Highest performance configuration for writes
• Lowest cost per unit of data stored
• All disk capacity is used to store data (none needed for fault tolerance)
The disadvantages of RAID 0 are as follows:
• All data on the logical drive is lost if a physical disk fails.
• Online spare disks are not available.
• Data preservation by backing up to external physical disks only.
RAID 1: Disk Mirroring
In this configuration, only two physical disks are present in the array. Data is duplicated from
one disk onto the other, creating a mirrored pair of disk drives, but there is no striping of data
(see Figure 2-2: “Disk Drive Mirroring of P1 onto P2 (RAID 1)”, ).
RAID 0: No Fault Tolerance 15