Storage Terminology

ACCESS CONTROL:

General term for a group of security techniques such as using passwords or smart cards to limit access to a computer or network only to authorized users.

AVAILABILITY:

 The accessibility of a computer system or network resource.

BACKUP/RESTORE:

The act of copying files and databases to protect them in the event of a system failure or similar catastrophe and retrieving them at a later date.

BBU (Battery Backup Unit):

A battery-operated power supply used as an auxiliary source of electricity in the event of power failure. The battery guarantees no lost writes and orderly transitions or shutdowns during power outages.

BCV (Business Continuance Volumes):

Business Continuance Volumes are copies of active production volumes that can be used to run simultaneous tasks in parallel with one another. This gives customers the ability to do concurrent operations, such as data warehouse loads and refreshes or point-in-time backups, without affecting production systems.

BUS:

A transmission channel in a computer or on a network that carries signals to and from devices attached to the channel.

BUSINESS CONTINUANCE:

The technique of ensuring that a business is able to weather a natural or man-made catastrophe through the deployment of fault-tolerant and redundant hardware and software systems.

CACHING:

A method of temporarily storing frequently accessed data in RAM or an special area of a hard disk drive, to speed processing. With sufficient storage-processor and backup memory, a storage system also supports write caching temporary storage where data is held for a short time before being written on disk for permanent storage.

CHANNEL:

A high bandwidth connection between a processor and other processors or devices.

CHECKSUM:

A number of bits that is transmitted with data so that the receiving device can verify the accuracy of the data that it received. If the number of bits that arrives is the same that is sent, the transmission is believed to be complete.

CLUSTER:

A collection of high-performance, interconnected computer servers working together as a single processing resource in an application environment to provide scalable, high availability to both users and applications.

CONNECTIVITY:

The ability of hardware devices or software to communicate with other hardware or software.

CROSS-PLATFORM:

Systems that are operating-system independent and can operate across different system platforms.

DATA INTEGRITY:

The accuracy of data after being transmitted or processed.

DATA MART:

A repository of data, often a scale-down data warehouse, usually tailored to the needs of a specific group within an organization

DATA MINING:

Using advanced statistical tools to identify commercially useful patterns in databases.

DATA WAREHOUSE:

A very large repository of data comprising nearly all of a company’s information.

DEBUG:

To detect, locate, and correct problems in a program or malfunctions in software. (Troubleshoot in a hardware context.)

DEFRAG:

To improve file access by rearranging data so that whole files are stored in contiguous sectors on a hard disk.

DEVICE:

A computer subsystem such as a printer, serial port, disk drive, or video adapter. Frequently, devices require their own controlling software (device drivers) to communicate with the computer system.

DISASTER RECOVERY:

Preventative measures using redundant hardware, software, data centers and other facilities to ensure that a business can continue operations during a natural or man-made disaster and if not, to restore business operations as quickly as possible when the calamity has passed.

DISK CONTROLLER:

The hardware that controls the writing and reading data to and from and to a disk drive. It can be used with floppy disks or hard drives. It can be hard-wired or built into a plug-in interface board.

DISK MIRRORING:

Disk mirroring provides the highest data availability for mission-critical applications by creating two copies of data on separate disk drives. The technique ensures both the highest availability and highest system performance.

DISK STRIPING:

Combining a set of same-size disk partitions from 2 to 32 separate disks into a single volume that virtually "stripes" these disks in a way that the operating system recognizes as a single drive. Disk striping enhances performance by enabling multiple I/O operations in the same volume to proceed simultaneously.

DISK STRIPING with PARITY:

Preserving parity information across a disk stripe so that if one disk partition fails, its data can be re-created with information stored across the remaining portions of the disk stripe.

E-INFOSTRUCTURE:

A shared foundation of technologies, tools, services, and intellectual capital that enables an uninterrupted flow of information

ERROR CORRECTION CODING (ECC):

An encoding method that detects and corrects errors at the receiving end of data transmission. ECC is used by most modems.

FABRIC:

A Fibre Channel topology with one or more switching devices.

FAILOVER:

Data is immediately and nondisruptively routed to an alternate data path or device in the event of an event of an adapter, cable, channel controller or other device.

FAST DUMP/RESTORE (FDR):

A family of mainframe-based backup/restore utilities that use Symmetrix with existing mainframe infrastructures to provide a comprehensive suite of fast, nondisruptive information protection solutions for both mainframe and open systems environments.

FAULT TOLERANCE:

A computer or operating system’s ability to respond to a catastrophic event like a power outage or hardware failure so that no data is lost or corrupted.

FIBREALLIANCE:

The FibreAlliance is an open association of industry-leading Fibre Channel vendors committed to accelerating the adoption rate of storage area networks (SANs). Members are working to develop a framework specification within which multiple vendors can develop integrated management environments for enterprise SAN customers.

FIBER CHANNEL ARBITRATED LOOP (FC-AL):

FC-AL places up to 126 devices on a loop to share bandwidth. Typically, this is done using a star layout that is logically a loop, employing a Fibre Channel hub. This allows IT managers to add or remove devices without having to bring the entire loop down.

FIBRE CHANNEL (FC):

Fibre channel is nominally a one-gigabit-per-second data transfer interface technology, although the specification allows data transfer rates from 133 megabits per second up to 4.25 gigabits per second. Data can be transmitted and received at one-gigabit-per-second simultaneously. Common transport protocols, such as Internet Protocol (IP) and Small Computer System Interface (SCSI), run over Fibre Channel. Consequently, high-speed I/O and networking can stem from a single connectivity technology.

HARD DISK:

A mass storage device for computer data that consists of a hermetically sealed enclosure that holds stacked, rotating, magnetizable disks accessed by multiple read/write heads.

HARDWARE RAID:

Dual-storage processors that improve data availability and performance create data protection information and transfer it to the disk drives. They are located in an external storage subsystem, freeing the CPU from performing RAID parity, striping, and rebuild overhead calculations. This intelligent circuit board controls the disk drives.

HBA (Host Bus Adapter):

An SCSI-2 adapter that plugs into a host and lets the host communicate with a device. The HBA usually performs the lower level of the SCSI protocol and normally operates in the initiator role.

HOST:

A computer server, typically networked, that runs applications used by or from other computers (e.g., web servers, file servers, and application servers).

HOT SPARE:

In RAID systems, a spare drive in the disk array that is configured as a backup for rebuilding data in the event another drive fails.

HOT SWAPPING:

The process of removing and replacing a failed system component while the system remains online.

HUB:

A device joining communications lines at a central location, providing a common connection to all devices on the network.

INFORMATION MANAGEMENT:

The entire process of defining, evaluating, protecting, and distributing data within an organization.

INFRASTRUCTURE:

The basic, fundamental architecture of a computer system. The infrastructure determines how the system functions and how flexible it is in meeting future demands.

INTELLIGENT:

A device is intelligent when it is controlled by one or more processors integral to the device.

INTEROPERABILITY:

The ability of hardware and software made by a variety of different manufacturers to work seamlessly together.

JBOD (Just a Bunch of Disks):

A group of hard disks, usually without intelligence (processors).

LINK:

A connection between two Fibre Channel ports.

LUN (Logical Unit Number): An encoded 3-bit identifier used on an SCSI bus to distinguish among up to eight devices (logical units) with the same SCSI ID. An LUN is an indivisible unit presented by a storage device to its host. LUNs are assigned to each disk drive in an array so the host can address and access the data on those devices.

LUN Masking:

An array security feature that lets a server access only its own and no other LUNs on a Fibre Channel. Each LUN can specify what host or combination of hosts has access to that LUN.

MAINFRAME:

A computer primarily used by Global 2000 corporations for large-scale commercial applications. A mainframe is capable of supporting many users from many terminals.

MODULARITY:

An approach to developing hardware or software that breaks projects into smaller units (or modules) that are deliberately designed as standalone units that can work with other sections of the program. The same module can perform the same task in another or several other programs or components. Modifying the way that module works will have no adverse affects on the other components of a program.

MULTIPATHING:

Multipathing allows for two or more data paths to be simultaneously used for read/write operations, enhancing performance by automatically and equally dispersing data access across all the available paths.

NAME SERVICES LOGIN:

Worldwide-exclusive names that allow a device to log into the switch.

NONVOLATILE:

Data in memory, cache and other electronic repositories are protected by a battery backup system to prevent their loss in the event of a power failure.

OLTP:

Online Transaction Processing is a system that processes transactions the instant the computer receives them and updates master files immediately. OLTP is essential for good financial record keeping and inventory tracking.

PARITY:

A data-error-checking procedure where the number of 1s must always be the same—either even or odd— for each group of bits submitted without error. Parity information is saved and compared with each subsequent calculations of whether the number is odd or even.

PARITY BIT:

An extra bit used in checking for errors in transferred groups of data bits. In modem communications, it is used to check the accuracy of each transmitted character. In RAM, a parity bit is used to check the accuracy with which each byte is stored.

PB (PetaByte):

1 quadrillion bytes or one thousand terabytes.

PORT:

On a computer, it is a physical connecting point to which a device is attached.

PROTOCOL:

A set of rules or standards intended to enable computers to communicate.

RAID (Redundant Array of Independent Disks):

Data is stored on multiple magnetic or optical disk drives to increase output performance and storage capacities and to provide varying degrees of redundancy and fault tolerance. Instead of storing valuable data on a single hard disk that could fail at any time, RAID makes sure a backup copy of all information always exists by spreading data among multiple hard disks.

RAID Levels:

Different levels offer trade-offs among speed, reliability, and cost.

• Level 0 is disk striping only for better performance. Its data transfer and I/O rates are very high, but it provides no safeguards against data failure.

• Level 1 uses disk mirroring. All data is duplicated on two drives, offering the highest data reliability. Its data transfer rate is higher than single disk for read and similar for write. Its I/O rate is twice that of single disk for read but similar for write.

• Level 1/0 is a combination of Levels 1 and 2, mirroring and striping. It offers the same data reliability as RAID 1. Its data-transfer and I/O rates are very high, but slower than RAID 0 for writes

• Level 3 stripes data across three or more drives. All drives operate in parallel to achieve the highest data transfer rate. Parity bits are stored on separate, dedicated drives. Its I/O rate is similar to single disk.

• Level 5 is the most widely used. Data is striped across three or more drives for high performance. The parity bits from two drives are stored on a third drive. Its data reliability is similar to RAID 3. Its data transfer and I/O rates are very high for read, but slower than single disk for write.

READ-ONLY:

Data can be retrieved (read) but not altered (written).

REDUNDANT:

Backup arrays, drives, disks or power supplies that duplicate functions performed elsewhere.

ROBUST:

Able to function or continue to function well in a variety of unanticipated situations.

SCALABILITY:

The capacity of hardware, software and networks to change size according to the number of users that they accommodate. Most often, scalability refers to the capacity to expand rather than shrink.

SCSI:

Small Computer System Interface. The standard set of protocols for host computers communicating with attached peripherals. SCSI allows connection to as many as six peripherals including printers, scanners, hard drives, zip drives, and CD-ROM drives.

SCSI-2:

An enhanced ANSI standard for SCSI standard for SCSI buses. It offers increased data width, increased speed, or both.

SCSI bus:

A parallel bus that carries data and control signals from SCSI devices to an SCSI controller.

SOFTWARE RAID:

Uses the server processor to perform RAID calculations. Host CPU cycles that read and write data from and to disk are taken away from applications. Software RAID is less costly than dedicated hardware RAID storage processors, but its data protection is less efficient and reliable.

SWITCH:

A network device that selects a path or circuit for sending a data between destinations.

TERABYTE (TB):

A thousand billion bytes or one thousand gigabytes.

THROUGHPUT:

In computers, it is a measurement of the amount of work that can be processed within a set time period. In networking, it is a measurement of the amount of data that can be successfully transferred with a set time period.

VOLUME:

A virtual disk into which a file system, database management system or other application places data. A volume can be a single disk partition or multiple partitions on one or more physical drives.

WORKLOAD BALANCING:

It’s a technique that ensures no one data path can become overloaded while others have underutilized bandwidth causing an I/O bottleneck. When one or more paths become busier than others, I/O traffic shifts from the busy paths to the others, further enhancing throughput over the already efficient multipathing method.

WRITE-CACHE:

A form of temporary storage in which data is stored (or cached) in memory before being written to a hard disk for permanent storage. Caching enhances overall system performance by decreasing the number of times the central processor reads and writes to a hard disk.

WRITE-MODE:

The state in which a program can write (record) information in a file. In the write-mode, the user is permitted to make changes in existing information.

ZONING:

Several devices are grouped by function or by location. All devices connected to a connectivity product may include configuration of one or more zones. Devices in the same zone can see each other; devices in different zones cannot.

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