HP DL160 HP StorageWorks All-in-One Storage Manager user guide (452695-004, No - Page 25
Table 6 Descriptions of RAID levels, Description, RAID level
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For more information on the different RAID levels, see Table 6. Table 6 Descriptions of RAID levels RAID level Description No RAID Offers no protection against disk failure. If a disk drive fails, data is lost. RAID 0 - Striping (No Fault Tolerance) Offers the greatest capacity and performance without data protection. If you select this option, you will experience data loss if a hard drive that holds the data fails. However, because no logical drive capacity is used for redundant data, this method offers the best capacity. This method offers the best processing speed by reading two stripes on different hard drives at the same time and by not having a parity drive. RAID 1 - Mirroring Offers a good combination of data protection and performance. RAID 1 or drive mirroring creates fault tolerance by storing duplicate sets of data on a minimum of two hard drives. There must be an even number of drives for RAID 1. RAID 1 and RAID 1+0(10) are the most costly fault tolerance methods because they require 50 percent of the drive capacity to store the redundant data. RAID 1 mirrors the contents of one hard drive in the array onto another. If either hard drive fails, the other hard drive provides a backup copy of the files and normal system operations are not interrupted. RAID 1+0 - Mirroring and Striping Offers the best combination of data protection and performance. RAID 1+0 or drive mirroring creates fault tolerance by storing duplicate sets of data on a minimum of four hard drives. There must be an even number of drives for RAID 1+0. RAID 1+0(10) and RAID 1 are the most costly fault tolerance methods because they require 50 percent of the drive capacity to store the redundant data. RAID 1+0(10) first mirrors each drive in the array to another, and then stripes the data across the mirrored pair. If a physical drive fails, the mirror drive provides a backup copy of the files and normal system operations are not interrupted. RAID 1+0(10) can withstand multiple simultaneous drive failures, as long as the failed drives are not mirrored to each other. RAID 5 - Distributed Data Guarding Offers the best combination of data protection and usable capacity while also improving performance over RAID 6. RAID 5 stores parity data across all the physical drives in the array and allows more simultaneous read operations and higher performance than data guarding. If a drive fails, the controller uses the parity data and the data on the remaining drives to reconstruct data from the failed drive. The system continues operating with a slightly reduced performance until you replace the failed drive. RAID 5 can only withstand the loss of one drive without total array failure. It requires an array with a minimum of three physical drives. Usable capacity is N-1 where N is the number of physical drives in the logical array. RAID 6- Advanced Data Guarding (ADG) Offers the best data protection and is an extension of RAID 5. RAID 6 uses multiple parity sets to store data and can therefore tolerate up to 2 drive failures simultaneously. RAID 6 requires a minimum of 4 drives and is available only if the controller has an enabler. Writer performance is lower than RAID 5 due to parity data updating on multiple drives. It uses two disk for parity; its fault tolerance allows two disks to fail simultaneously. Usable capacity is N-2 where N is the number of physical drives in the logical array. All-in-One Storage Manager 25