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cable plant[Network] All of an installation's passive communications elements (e.g., optical fiber, twisted pair, or coaxial cable, connectors, splices, etc.) between transmitters and receivers. cache1. [Computer System] To store data temporarily for expedited access. 2. [Computer System] The location in which data is stored temporarily. There are a variety of cache types. Read cache holds data in anticipation that it will be requested. Write cache holds data written by a client until it can be stored on other (typically slower) storage media such as disk or tape. See buffer, disk cache, write back cache, write through cache. canister[Storage System] An enclosure for a single disk or tape. Canisters are usually designed to mount in shelves that supply power, cooling, and I/O bus services to the devices. Canisters are used to minimize RF emissions and to simplify insertion and removal of devices in multi-device storage subsystems. See shelf. carousel[Data Recovery] A media handling robot in which the media are stored in and selected from a rotating wheel. Carrier Sense Multiple Access with Collision Detection (CSMA/CD)[Network] A physical layer data transmission protocol used in Ethernet and fast Ethernet networks. Carrier sense refers to arbitration for a shared link. Unlike "always on" physical protocols, carrier sense protocols require a node wishing to transmit to wait for the absence of carrier (indicating that another node is transmitting) on the link. Multiple access refers to the party line nature of the link. A large number of nodes (up to 500 in the case of Ethernet) share access to a single link. Collision detection refers to the possibility that two nodes will simultaneously sense absence of carrier and begin to transmit, interfering with each other. Nodes are required to detect this interference, and cease transmitting. In the case of Ethernet, each node detecting a collision is required to wait for a random interval before attempting to transmit again. cascading[Fibre Channel] The process of connecting two or more Fibre Channel hubs or switches together to increase the number of ports or extend distances. catalog1. [Data Recovery] A stored list of backed up files and directories and the locations (media identifiers) of the backup copies. 2. [File System] A persistent data structure used by some file systems to keep track of the files they manage. certificate[Data Security] A data structure signed with a digital signature that is based a public key and which asserts that the key belongs to a subject identified in the structure. Certificate Revocation List (CRL)[Data Security] A time-stamped list of certificates, signed by the issuing Certification Authority, that have been revoked by that CA. The CRL is made available to entities that need to rely on a certificate for authentication. Certification Authority (CA)[Data Security] In a Public Key Infrastructure (PKI), the authority and organization responsible for issuing and revoking user certificates, and ensuring compliance with the PKI policies and procedures. chain of custody[Legal] The documentation of the movement and possession of a piece of evidence at all times from its collection through analysis to presentation in court. challenge[Data Security] A step in an authentication dialog that must be answered using either a secret or process assumed to be known only by the other party. A challenge can be as simple as "What's your password?" or as complex as "Send me the result of a retinal scan of your right eye." Challenge Handshake Authentication Protocol (CHAP)[Data Security] A password-based authentication protocol that uses a challenge to verify that a user has access to a system; a hash of the supplied password with the challenge is sent for comparison so the cleartext password in never sent over the connection. changed block point in time copy[Storage System] Any of a class of point in time copy implementations or the resulting copies in which the copy and its source share storage for portions (usually blocks) of the copy that are not subsequently modified (in the source, or in the copy if the copy is writeable). Storage is physically copied only as a consequence of modifications (to the source, or to the copy if the copy is writeable). A changed block copy occupies only the storage necessary to hold the blocks of storage that have been changed since the point in time at which the copy logically occurred. channel1. [Storage System] The electrical circuits that sense or cause the state changes in recording media and convert between those state changes and electrical signals that can be interpreted as data bits. 2. [Computer System] Synonym for I/O bus. The term channel has other meanings in other branches of computer technology. The definitions given here are commonly used when discussing storage and networking. See device channel, device I/O bus, I/O bus, host I/O bus. character1. [Computer System] Synonym for byte. 2. [Fibre Channel] A 10-bit information unit transmitted and received by FC-1, consisting of 8 bits of data encoded as a 10 bit transmission character using 8B/10B encoding Some transmission characters used in FC-1 correspond to special codes and some 10 bit sequences represent invalid transmission characters. checkpoint1. [Data Recovery] The recorded state of an application at an instant of time, including data, in-memory variables, program counter, and all other context that would be required to resume application execution from the recorded state. 2. [File System] An activity of a file system, such as the High Performance File System, (HPFS) or the Andrew File System (AFS), in which cached metadata (data about the structures of the file system) is periodically written to the file system's permanent store, allowing the file system to maintain consistency if an unexpected stop occurs. cipher[Data Security] Any cryptographic system in which arbitrary symbols or groups of symbols represent units of plain text, or in which units of plain text are rearranged, or both. Cipher Block Chaining (CBC)[Data Security] A block cipher mode of operation, in which each block of plaintext is XORed with the previous ciphertext block before being encrypted, making each ciphertext block dependent on all preceding plaintext blocks. Class 1[Fibre Channel] A connection-oriented class of Fibre Channel communication service in which the entire bandwidth of the link between two ports is dedicated for communication between the ports and not used for other purposes. Class 1 is also known as dedicated connection service, and is not widely implemented. See intermix. Class 2[Fibre Channel] A connectionless Fibre Channel communication service which multiplexes frames from one or more N_Ports or NL_Ports. Class 2 frames are explicitly acknowledged by the receiver, and notification of delivery failure is provided. This class of service includes end to end flow control. Class 3[Fibre Channel] A connectionless Fibre Channel communication service which multiplexes frames to or from one or more N_Ports or NL_Ports. Class 3 frames are datagrams, that is they are not explicitly acknowledged, and delivery is on a "best effort" basis. classified information[Data Security] Information that an appropriate agency has determined to require protection against unauthorized disclosure and has caused to be marked to indicate its classified status. class of service1. [Network] A mechanism for managing traffic in a network by specifying message or packet priority or delivery acknowledgement. Network mechanisms include identification and grouping of data packets based on a priority label (in the packet header) or via mechanisms such as "per hop behavior", defined by the IETF's Differentiated Services. 2. [Fibre Channel] The characteristics and guarantees of the transport layer of a Fibre Channel circuit. Fibre Channel classes of service include connection-based services (Class 1), acknowledged frame delivery with end to end flow control (Class 2), and packetized frame datagrams (Class 3). Different classes of service may simultaneously exist in a fabric. The form and reliability of delivery in Class 3 circuits may vary with the topology. cleartext[Data Security] Alternative term for plaintext. Stating that data is in cleartext implies that the data is not scrambled or rearranged, and is in its raw form. client1. [Computer System] An intelligent device or system that requests services from other intelligent devices, systems, or appliances. See server. 2. [General] An asymmetric relationship with a second party (a server) in which the client initiates requests and the server responds to those requests. cluster[Computer System] A collection of computers that are interconnected (typically at high speeds) for the purpose of improving reliability, availability, serviceability, load balancing and/or performance. Often, clustered computers have access to a common pool of storage, and run special software to coordinate the component computers' activities. coaxial cable[Network] An electrical transmission medium consisting of two concentric conductors separated by a dielectric material with the spacings and material arranged to give a specified electrical impedance. See triaxial cable . code bit[Computer System] A bit (binary digit) of an encoded datum. Sequences of code bits make up symbols, each of which corresponds to a data element (word, byte, or other unit). code byte[Computer System] A byte of an encoded datum. Sometimes called a symbol. Code bytes are the output of encoding or encryption processes. In communication theory contexts, a code byte is often referred to as a code word. See data byte. code violation[Fibre Channel] The error condition that occurs when a received transmission character cannot be decoded into a valid data byte or special code using the validity checking rules specified by the transmission code. cold swap[Computer System] The substitution of a replacement unit (RU) in a system for a defective one, where external power must be removed from the system in order to perform the substitution. A cold swap is a physical substitution as well as a functional one. See automatic swap, hot swap, warm swap. comma character1. [Fibre Channel] Either of the seven bit sequences 0011111 or 1100000 in an encoded stream. Command Descriptor Block (CDB)[SCSI] A sequence of bytes that defines a single SCSI command sent to a SCSI target. Command Line Interface (CLI)[Computer System] A form of human interface to intelligent devices characterized by non-directive prompting and character string user input. CLIs are very useful for scripting and other administrative purposes, but are usually perceived by end users to be more difficult to comprehend and use than graphical user interfaces (GUIs). command security[SCSI] The application of security techniques such as authentication, integrity checking and encryption to individual SCSI commands. Common Criteria (CC)[Data Security] A multi-part International Standard that is meant to be used as the basis for evaluation of security properties of IT products and systems. The CC is specified in ISO/IEC 15408-1:1999, ISO/IEC 15408-2:1999, and ISO/IEC 15408-3:1999. Common Information Model (CIM)[Data Management] [Network] An object oriented description of the entities and relationships in a business' management environment maintained by the Distributed Management Task Force. CIM is divided into a Core Model and Common Models. The Core Model addresses high-level concepts (such as systems and devices), as well as fundamental relationships (such as dependencies). The Common Models describe specific problem domains such as computer system, network, user or device management. The Common Models are subclasses of the Core Model and may also be subclasses of each other. Common Internet File System (CIFS)[Network] A network file system access protocol primarily used by Windows clients to communicate file access requests to Windows servers. CIFS was originally called Server Message Block (SMB). Today, other implementations of the CIFS protocol allow other clients and servers to use it for intercommunication and interoperation with Microsoft operating systems. Common Management Information Protocol (CMIP)[Management] [Network] A network management protocol built on the Open Systems Interconnection (OSI) communication model. communication circuit1. [Fibre Channel] A bidirectional path for message exchange within a Fibre Channel fabric. 2. [Network] A specific logical or physical path between two points over which communications occur. communications security[Network] [Data Security] Protection of information while it's being transmitted, particularly via telecommunications. A particular focus of communications security is message authenticity. Communications security may include cryptography, transmission security, emission security, and physical security. complex array[Storage System] A disk array whose control software protects and maps data according to more complex algorithms than those of the Berkeley RAID Levels. The most common complex arrays are multi-level disk arrays, which perform more than one level of data address mapping, and adaptive arrays, which are capable of changing data address mapping dynamically. compression[General] The process of encoding data to reduce its size. Lossy compression (i.e., compression using a technique in which a portion of the original information is lost) is acceptable for some forms of data (e.g., digital images) in some applications, but for most IT applications, lossless compression (i.e., compression using a technique that preserves the entire content of the original data, and from which the original data can be reconstructed exactly) is required. compliance1. [General] The state of being in accordance with a standard, specification, or clearly defined requirements. 2. [Legal] The state of being in accordance with legal requirements. The "compliance market" is centered around storage and systems that support the retention and discovery of data as required by law or regulation. compromise[Data Security] An incident that subjects data to unauthorized disclosure, modification, destruction, or loss. computer security[Data Security] Measures and controls that ensure confidentiality, integrity, and availability of information system assets including hardware, software, firmware, and information being processed, stored, and communicated. concatenation[Network] [Storage System] A logical joining of two series of data, usually represented by the symbol "|". In data communications, two or more datums are often concatenated to provide a unique name or reference (e.g., S_ID | X_ID). Volume managers concatenate disk address spaces to present a single larger address spaces. concurrency[Computer System] The property of overlapping in time, often in reference to the execution of I/O operations or I/O requests. concurrent copy[Storage System] A hybrid point in time copy mechanism which creates a split mirror copy by copying blocks from the source as they are requested by the host, while copying so-far unrequested blocks in the background until the mirror is complete. A concurrent copy initially occupies at least the amount of storage required to hold accessed blocks and grows to occupy as much storage as the copy source. concurrent operations[Computer System] Operations that overlap in time. The concept of concurrent I/O operations is central to the use of independent access arrays in throughput-intensive applications. conditioning[General] The processing of a signal for the purpose of making it conform more closely to an ideal. Power conditioning is used to minimize voltage and frequency variations in an external power. Signal conditioning is used to reduce noise in logic or data signals. confidentiality[Data Security] The property that data cannot be accessed by unauthorized parties. Confidentiality may be created by the use of encryption or access controls. configuration1. [Storage System] The process of installing or removing hardware or software components required for a system or subsystem to function. 2. [Storage System] Assignment of the operating parameters of a system, subsystem or device, such as designating a disk array's member disks or extents and parameters such as stripe depth, RAID model, cache allowance, etc. 3. [Storage System] The collection of a system's hardware and software components and operating parameters. See array configuration, physical configuration. configuration management[General] The management of system features and behaviors through the control of changes made to hardware, software, firmware documentation and related resources throughout the life cycle of an information system. connection1. [Fibre Channel] Short form of dedicated connection. 2. [iSCSI] A communication path between the initiator and target using a TCP/IP connection. In iSCSI, one or more connections make up a session. Connections carry control messages, SCSI commands, parameters, and data within iSCSI PDUs. connection identifier[iSCSI] An identifier generated by the initiator and sent to the target upon logging in or out, that uniquely identifies each connection within a session. connection initiator[Fibre Channel] An N_Port that initiates a Class 1 connection with a destination N_Port through a connect-request and which receives a valid response from the destination N_Port to establish the connection. connection recipient[Fibre Channel] An N_Port that receives a Class 1 connect-request from a connection initiator and accepts the connection request by transmitting a valid response. connectionless buffer[Fibre Channel] A receive buffer used in a connectionless service that is capable of receiving connectionless frames. connectionless frame[Fibre Channel] A frame used in a connectionless service (i.e., Class 1 frames with SOF(C1)., Class 2, and Class 3 frames referred to individually or collectively) connectionless integrity service[Data Security] A security service that provides data integrity service for an individual IP datagram by detecting modification of the datagram without regard to the ordering of the datagram in a stream of datagrams. connectionless service[Fibre Channel] Communication between two N_Ports or NL_Ports without a dedicated connection. consistency group[Storage System] A collection of replication sets grouped together to ensure write order consistency across all the replication sets' primary volumes. An operation on a consistency group, such as changing replication from asynchronous to synchronous, applies to all the replication sets within the consistency group, and consequently their volumes. console1. [Computer System] A device for graphical or textual visual output from a computer system. 2. [Computer System] In systems, network and device management, an application that provides graphical and textual feedback regarding operation and status, and that may accept operator commands and input influencing operation and status. Sophisticated consoles designed for the management of many systems from one location are sometimes called enterprise management consoles. Continuous Data Protection (CDP)[Data Recovery] A class of mechanisms that continuously capture or track data modifications enabling recovery to previous points in time. continuously increasing relative offset[Fibre Channel] A transmission control algorithm in which the frames containing the subblocks that comprise a block of information are transmitted strictly in the order of the subblocks. Continuously increasing relative offset offers simpler reassembly and detection of lost frames compared to random relative offset. control software[Storage System] A body of software that provides common control and management for one or more disk arrays or tape arrays. Control software presents the arrays of disks or tapes it controls to its operating environment as one or more virtual disks or tapes. Control software may execute in a disk controller or intelligent host bus adapter, or in a host computer. When it executes in a disk controller or adapter, control software is often referred to as firmware. controller1. [Storage System] The control logic in a disk or tape that performs command decoding and execution, host data transfer, serialization and deserialization of data, error detection and correction, and overall management of device operations. 2. [Management] The control logic in a storage subsystem that performs command transformation and routing, aggregation (RAID, mirroring, striping, or other), high-level error recovery, and performance optimization for multiple storage devices.
controller based array
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