Intel AFCSASRISER User Guide - Page 31

RAID Configuration Strategies The most important factors in RAID array configuration are: • Virtual disk availability (fault tolerance) • Virtual disk performance • Virtual disk capacity You cannot configure a virtual disk that optimizes all three factors, but it is easy to choose a virtual disk configuration that maximizes one factor at the expense of another factor. For example, RAID 1 (mirroring) provides excellent fault tolerance, but requires a redundant drive. The following subsections describe how to use the RAID levels to maximize virtual disk availability (fault tolerance), virtual disk performance, and virtual disk capacity. Maximizing Fault Tolerance Fault tolerance is achieved through the ability to perform automatic and transparent rebuilds using hot-spare drives and hot swaps. A hot-spare drive is an unused online available drive that the RAID controller instantly plugs into the system when an active drive fails. After the hot spare is automatically moved into the RAID array, the failed drive is automatically rebuilt on the spare drive. The RAID array continues to handle requests while the rebuild occurs. A hot swap is the manual substitution of a replacement unit in a disk subsystem for a defective one, where the substitution can be performed while the subsystem is running hot-swap drives. Auto-Rebuild in the WebBIOS Configuration Utility allows a failed drive to be replaced and automatically rebuilt by "hot swapping" the drive in the same drive bay. The RAID array continues to handle requests while the rebuild occurs, providing a high degree of fault tolerance and zero downtime. Table 9. RAID Levels and Fault Tolerance RAID Level Fault Tolerance 0 Does not provide fault tolerance. All data is lost if any drive fails. Disk striping writes data across multiple disk drives instead of just one disk drive. It involves partitioning each drive storage space into stripes that can vary in size. RAID 0 is ideal for applications that require high bandwidth but do not require fault tolerance. 1 or Provides complete data redundancy. If one drive fails, the contents of the other drive can IME be used to run the system and reconstruct the failed drive. The primary advantage of disk mirroring is that it provides 100 percent data redundancy. Since the contents of the drive are completely written to a second drive, no data is lost if one of the drives fails. Both drives contain the same data at all times. RAID 1 or IME is ideal for any application that requires fault tolerance and minimal capacity. 5 Combines distributed parity with disk striping. Parity provides redundancy for one drive failure without duplicating the contents of entire disk drives. If a drive fails, the RAID controller uses the parity data to reconstruct all missing information. In RAID 5, this method is applied to the entire drive or stripes across all disk drives in an array. Using distributed parity, RAID 5 offers fault tolerance with limited overhead. Intel® RAID Software User's Guide 19