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RAID Terminology OverviewRedundant array of independent disks (RAID) is a storage technology used to improve the processing capability of storage systems. This technology is designed to provide reliability in disk array systems and to take advantage of the performance gains offered by an array of multiple disks over single-disk storage. RAIDs two primary underlying concepts are:
In the event of a disk failure, disk access continues normally and the failure is transparent to the host system. Logical Drive A logical drive is an array of independent physical drives. Increased availability, capacity, and performance are achieved by creating logical drives. The logical drive appears to the host the same as a local hard disk drive does. Logical Volume A logical volume is composed of two or more logical drives. The logical volume can be divided into a maximum of 32 partitions for Fibre Channel. During operation, the host sees a nonpartitioned logical volume or a partition of a logical volume as one single physical drive. Local Spare Drive IA local spare drive is a standby drive assigned to serve one specified logical drive. When a member drive of this specified logical drive fails, the local spare drive becomes a member drive and automatically starts to rebuild. Global Spare Drive A global spare drive does not only serve one specified logical drive. When a member drive from any of the logical drives fails, the global spare drive joins that logical drive and automatically starts to rebuild. Channels You can connect up to 15 devices (excluding
the controller itself) to a SCSI channel when the Wide function is enabled
(16-bit SCSI). You can connect up to 125 devices to an FC channel in loop
mode. Each device has a unique ID that identifies the device on the SCSI
bus or FC loop. |