P parity A form of error correcting redundancy used to re-create the data of a failed disk drive in a RAID 3, 4, or 5 set. See also RAID 3; RAID 4; RAID 5; redundancy. Glossary-5 Glossary Glossary partition A subdivision of a disk or storage area. There are three main types of partitions: 1 A portion of a physical or virtual disk drive that functions as a separate unit. A single disk drive can be divided into several partitions, each of which the OS sees as a separate device with its own volume name (such as D:, E:, F:, and so on). These partitions are usually created by the OS. 2 Contiguous storage space produced during the RAID creation process. When a controller creates an array, it automatically converts some or all of the free space on a disk drive into one or more partitions. These partitions are not seen by the OS. Rather, they are the building blocks of a virtual disk. This virtual disk is seen by the OS as a single disk drive. Depending on the type of RAID array created, the virtual disk may be larger than any of its component partitions. For example, a stripe set (RAID 0) created from two partitions presents a virtual disk drive almost two times larger than the individual partitions. Each of these partitions can be used by only one array at a time. 3 A subdivision of a virtual disk. Some RAID controllers allow you to divide the virtual disk into multiple parts, or partitions. Each partition is seen by the OS as a separate disk drive. See also array; free space. preferred owner When a storage system is in an active-active mode, a single controller has ownership of arrays and dedicated spares and is the preferred owner. If the controller fails, the other controller assumes temporary ownership of its resources. See also storage system. Glossary-6 Glossary Glossary R RAID 0 See stripe set (RAID 0). RAID 0/1 See stripe set of mirror sets (RAID 0/1). RAID 0/5 See stripe set of RAID 5 sets (RAID 50). RAID 1 See mirror set (RAID 1). RAID 3 A RAID 3 set is an array made up of three or more disk drives. It uses parallel access, meaning all member disk drives participate concurrently in every I/O operation directed at the array. Each virtual disk drive I/O operation is subdivided and distributed (striped) across all data disk drives; therefore, it uses small stripe depth. Parity check data is stored on a separate parity disk drive. See also chunk; partition; parity. RAID 4 A RAID 4 set is an array made up of three or more disk drives. Data blocks are distributed as with RAID 0 (disk striping). It differs from RAID 3 in two ways: 1) it normally uses independent access (rather than parallel access), meaning the array’s disk drives may operate independently of each other allowing multiple simultaneous read and write operations, and 2) stripe depth is larger than the virtual disk drive average I/O size. Parity check data is stored on a separate parity disk drive. See also chunk; par...

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