3Ware 9550SXU-8LP User Guide - Page 256

Chapter A. Glossary is running. However, RAID 5 initialization done through the 3ware BIOS does erase any existing data. • JBOD. An unconfigured single drive. The acronym is derived from "just a bunch of disks." Note that earlier versions of the 3ware RAID controller exported JBODs to the OS. By default, this is not the case in 9000-series controllers. However, a policy in 3BM can be set that allows JBODs to be seen by the OS. By default, individual drives must be configured as Single Disks in order to be made available to the OS. • 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 and 9590SE controllers. NCQ must be turned on in both the drive and the RAID controller. By default, the RAID unit's queue policy is disabled 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. 246 3ware Serial ATA RAID Controller User Guide