IBM 201 manual CRC see cyclic redundancy check CRU see customer-replaceable unit

connection-oriented network. A network which requires that a setup procedure be executed to establish an information channel between two logical nodes before they can interchange information.

control port. An alternate port that you can use to access the configuration when the data ports are not available.

control unit. A processor electronics assembly in a storage controller that exposes LUNs to the storage network and connects internally to the storage controllers disk drives. A storage controller can have 1 to n, but typically has one for each path group.

Copper Distributed Data Interface (CDDI). A proposed ANSI standard that defines a dual counter-rotating ring which operates at a rate of 100 Mbps over Category 5 copper wire.

coprocessor. A secondary processor used to speed up operations by handling some of the workload of the main CPU.

CRC (see cyclic redundancy check).

CRU (see customer-replaceable unit).

customer-replaceable unit (CRU). An assembly or part that a customer can replace in its entirety when any of its components fail. Contrast with field-replaceable unit (FRU).

cyclic redundancy check (CRC). (1) A redundancy check in which the check key is generated by a cyclic algorithm

(T). (2) A system of error checking performed at both the sending and receiving station after a block-check character has been accumulated.

D

daemon. A program that runs unattended to perform a standard service. Some daemons are triggered automatically to perform their task; others operate periodically.

data port. Ethernet ports used for storage-traffic and configuration purposes.

DASD queue. A queue that resides on a direct access storage device (DASD).

data store. An abstraction for a repository where data is kept, independent of underlying implementation. Data stores can be block based (a LUN or set of LUNs); file based (a local or remote file system); or relational (a database). Since IBM TotalStorage™ NAS family appliances are file based, all of their datastores must be kept in file systems, directories, or files which are kept on LUNs.

data bus. A bus used to communicate data internally and externally to and from a processing unit, storage, and peripheral devices (A). (See bus.)

data integrity. (1) The condition that exists as long as accidental or intentional destruction, alteration, or loss of data does not occur (T). (2) Preservation of data for its intended use.

DDP (see distributed data processing).

default route. A route, in the routing table, that is used when no other route is specified or appropriate.

device address. (1) In data communication, the identification of any device to which data can be sent or from which data can be received. (2) The first subchannel address recognized by a channel-attached device.

device identifier (ID). An 8-bit identifier that uniquely identifies a physical I/O device.

device parity protection. A function that protects data stored on a disk unit subsystem from being lost because of the failure of a single disk unit in the disk unit subsystem. When a disk unit subsystem has device parity protection and one of the disk units in the subsystem fails, the system continues to run. The disk unit subsystem reconstructs the data after the disk unit in the subsystem is repaired or replaced. See RAID and RAID-5.

DHCP (see Dynamic Host Configuration Protocol).

diagnostic diskette. A diskette containing diagnostic modules or tests used by computer users and service personnel to diagnose hardware problems.

IBM Glossary of Storage Networking Terms 111