3Ware 9550SXU-16ML User Guide - Page 244

Appendix A. Glossary „ Migration. The process of changing the characteristics of a unit. The change can be to expand the capacity of the array (OCE), change the stripe size of the array, change the array from redundant to non-redundant, or to change the array from non-redundant to redundant. „ Mirrored disk array. A pair of drives on which the same data is written, so that each provides a backup for the other. If one drive fails, the data is preserved on the paired drive. Mirrored disk arrays include RAID 1 and RAID 10. „ NCQ (Native Command Queuing). A feature designed to improve performance of SATA hard disks in some applications that require a lot of random access of data, such as server-type applications. When NCQ is enabled, the commands are reordered on the drive itself. NCQ must be supported by the drive and is only available on the 9550SX controller. NCQ must be turned on in both the drive and the RAID controller. By default, the RAID unit's queue policy is enabled when creating a unit. „ Non-redundant units. A disk array without fault tolerance (RAID 0, single disk, or JBOD.). „ OCE (Online Capacity Expansion). The process of increasing the size of an existing RAID unit without having to create a new array. See also migration. „ Parity. Information that the controller calculates using an exclusive OR (XOR) algorithm and writes to the disk drives in RAID 5 and RAID 50 units. This data can be used with the remaining user data to recover the lost data if a disk drive fails. „ PCB. Printed circuit board. „ P-Chip. PCI interface chip that connects the PCI bus to the high-speed internal bus and routes all data between the two using a packet switched fabric. There is one P-chip per controller card. „ Port ID. A unique identifier for a specific port in a system. Also called a drive ID. „ Rebuild task schedule. The specification for when rebuilding, may occur, including start time and duration. „ Rebuild a unit. To generate data on a new drive after it is put into service to replace a degraded drive in a fault tolerant unit (for example, RAID 1, 10, 5, or 50). „ Redundancy. Duplication of data on another drive or drives, so that it is protected in the event of a drive failure. „ Remove a drive. The process of making a drive unavailable to the controller. 234 3ware 9550SX Serial ATA RAID Controller User Guide