Connecting Hardware Devices Hard disk drives (HDDs) 85system and improves overall disk performance, it does not provide for dataredundancy.RAID 1 - Disk MirroringData written to one hard disk drive is simultaneously written to another hard disk drive. Ifone disk fails, the other disk can be used to run the system and reconstruct the faileddisk. Since the disk is mirrored, it does not matter if one on them fails because both diskscontain the same data at all times. Either disk can act as the operational disk. This levelprovides 100% redundancy because each drive in the system is duplicated. This type ofarray is used for read-intensive, fault tolerant required configurations. An even number ofdisks are required to configure this type of RAID level.RAID 5 - Disk Striping with Distributed ParityUses parity to generate redundancy data from two or more parent data sets. Paritystorage is rotated or distributed through the stripe of the disk array. This is an advantagein applications that require high read request rates with low write request rates such astransaction processing, office automation, and online customer service since paritygeneration can slow write operations down considerably. Three or more disks arerequired to configure this type of RAID level.To enable automatic recovery of a faulty disk array, you must specify the spare device inthe RAID configuration. If a drive fails, the RAID controller will automatically initiate arecovery sequence, bringing the spare device into service. For more information, refer tothe user’s guide that came with your RAID controller.RAID failuresThis section describes how the RAID configuration responds when a component failureoccurs.Striping configuration failure (RAID 0)A striping hard disk drive fault represents a critical RAID failure. To recover from astriping failure, replace the failed drive, then create a new RAID 0 and restore from offlinebackup.Mirrored drive RAID configuration failure (RAID 1)When a hard disk drive fails in a mirrored array, the sub-mirror that the drive is a part of istaken off-line. The system routes all data access to the remaining sub-mirror until thefailed drive is either hot-swapped or repaired. The performance of a degraded mirroredRAID is equal to the performance rendered by the remaining hard disk drive.Parity RAID configuration failure (RAID 5)The data in a RAID 5 array is kept in an encoded format, distributed across the number ofindependent drives in the array. Consequently, write operations on a parity RAID array
