Lenovo ThinkServer Storage SA120 (English) User Guide and Hardware Maintenance - Page 39

Chapter 4. Configuring RAID This topic provides information about RAID and the utility programs that are available for you to configure RAID. Note: After the storage array is identified by the server that it is connected to, refer to the documentation that comes with the RAID card or HBA installed in the server to configure the storage array. This topic contains the following items: • "About RAID" on page 27 • "Configuring the advanced SATA/SAS hardware RAID" on page 28 About RAID RAID, an acronym for Redundant Array of Independent Disks, is a technology that provides increased storage functions and reliability through redundancy. This is achieved by combining multiple hard disk drives into a logical unit, where data is distributed across the drives in one of several ways called RAID levels. When a group of independent physical hard disk drives are set up to use RAID technology, they are in a RAID array. This array distributes data across multiple hard disk drives, but the array appears to the host server as one single storage unit. Creating and using RAID arrays provides high performance, such as the expedited I/O performance, because several drives can be accessed simultaneously. RAID drive groups also improve data storage reliability and fault tolerance compared with single-drive storage systems. Data loss resulting from a drive failure can be prevented by reconstructing missing data from the remaining drives. The following list describes some of the most commonly used RAID levels: • RAID 0: block-level striping without parity or mirroring Simple stripe sets are normally referred to as RAID 0. RAID 0 uses striping to provide high data throughput, especially for large files in an environment that does not require fault tolerance. RAID 0 has no redundancy and it provides improved performance and additional storage without fault tolerance. Any drive failure destroys the array and the likelihood of failure increases with more drives in the array. RAID 0 does not implement error checking, so any error is uncorrectable. More drives in the array means higher bandwidth, but greater risk of data loss. RAID 0 requires a minimum number of two hard disk drives. • RAID 1: mirroring without parity or striping RAID 1 uses mirroring so that data written to one drive is simultaneously written to another drive. This is good for small databases or other applications that require small capacity but complete data redundancy. RAID 1 provides fault tolerance from disk errors or failures and continues to operate as long as at least one drive in the mirrored set is functioning. With appropriate operating system support, there can be increased read performance and only a minimal write performance reduction. RAID 1 requires a minimum number of two hard disk drives. © Copyright Lenovo 2014 27