HP Surestore Disk Array FC60 HP SureStore E Disk Array FC60 Service Manual (A5 - Page 400

parity A data protection technique that provides data redundancy by creating extra data based on the original data. Parity is calculated on each write I/O by doing a serial binary exclusive OR (XOR) of the data segments in the stripe written to the data disks in the LUN. Parity is used by RAID 5 LUNs to reconstruct data from a failed disk. peripheral device addressing (PDA) The addressing technique used by the host to address the disk array controllers. Because it is limited to addressing only eight LUNs, PDA has been superseded by VSA as the technique for addressing disk array LUNs. point-to-point One of three existing Fibre Channel topologies, in which two devices are directly connected by a link with no fabric, loop, or switching elements present. port The hardware entity that connects a device to a Fibre Channel topology. A device can contain one or more ports. primary disk array path or primary path The main data path used for host I/Os to a LUN. The primary path can be set using LVM. Because the disk array has two controllers, one controller acts as the primary path, and the other acts as the alternate path. If a failure occurs in the primary data path, the alternate path is used, maintaining access to the LUN. PROM (Programmable Read-Only Memory) SP-resident boot code that loads the SP microcode from one of the disk array's database drives when the disk array is powered up or when an SP is enabled. RAID An acronym for "Redundant Array of Independent Disks." RAID was developed to provide data redundancy using independent disk drives. RAID is essentially a method for configuring multiple disks into a logical entity (LUN) that appears to the host system as a single, contiguous disk drive. RAID uses features such data striping, disk mirroring, 400