A
Ablative - Method of recording optical data where holes are made in the media. Also called "pit forming"
Access - Read, write, or update information on a storage medium.
Access arm - Mechanical arm that moves read/write head across disk
Access time - Time interval between the instant at which a control unit initiates a call for data and the instant at which delivery of the data is completed. Access time equals latency plus transfer time.
Access Type - Specifies the percentage of random and sequential accesses performed in each I/O request. You can have 0% to 100% Random or Sequential accesses.
Address - character or group of characters that identifies a register, a particular part of storage (e.g. sector, track, block), or some other data source or destination
AIT - Advanced Intelligent Tape. A magnetic tape format developed by Sony that uses.
Appliance - An appliance is an intelligent device programmed to perform a single well-defined function, such as providing file, web, or print services. Appliances differ from general-purpose computers in that their software is normally customized for the function they perform, pre-loaded by a vendor, and not alterable by the user. Appliances are generally considered to be capable of performing their specialized functions at lower cost and with higher reliability than general-purpose servers. (Provided by SNIA - Storage Networking Industry Association).
Arbitrated loop - A loop type of typology where two or more ports can be interconnected, but only two ports at a time can communicate
Archive - A consistent copy of a collection of data, usually taken for the purpose of maintaining a long-term durable record of a business or application state. Archives are normally used for auditing or analysis rather than for application recovery. After files are archived, online copies of them are typically deleted, and must be restored by explicit action. (Provided by SNIA).
ATA - Interface spec for IDE drives.
Autoloader - A system that uses a robotic mechanism to automatically load and unload tape cartridges into a tape drive. Used to provide unattended data backup and file restoration.
Availability - The amount of time that a system is available during those time periods when it is expected to be available. Availability is often measured as a percentage of an elapsed year. For example, 99.95% availability equates to 4.38 hours of downtime in a year (0.0005 * 365 * 24=4.38) for a system that is expected to be available all the time. (Provided by SNIA).
Average Latency
Average Response Time (ms) - Average time between initiation and completion of an I/O operation in milliseconds.
Average Read Response Time (ms) - Average time between initiation and completion of a read operation.
Average Write Response Time (ms) - Average time between initiation and completion of a write operation.
Average Transaction Time (ms) - Average time between initiation of a request and completion of the corresponding reply.
Average Seek Time - The average time it takes for the read/write head to move to a specific location. To compute the average seek time, divide the time it takes to complete a large number of random seeks by the number of seeks performed.
 

B
Backup
* (noun) A collection of data stored on (usually removable) non-volatile storage media for purposes of recovery in case the original copy of data is lost or becomes inaccessible. Also called backup copy. To be useful for recovery, a backup must be made by copying the source data image when it is in a consistent state.
* (verb) The act of creating a backup. (Provided by SNIA)
Backup Window - The period of time available for performing a backup. Backup windows are typically defined by operational necessity. For example, if data is used from 8AM until midnight, then the window between midnight and 8AM is available for making backup copies. For consistent backups, data may not be altered while the backup is occurring, so in some cases a backup window is an interval of time during which data and applications are unavailable. (Provided by SNIA)
Bandwidth - Bandwidth is the total amount of data that can be transferred at one time between CPU and storage. Generally, bandwidth refers to large block data transfers and is usually measured in MB/sec. (For instance, the total bandwidth available on any given UltraSCSI bus is 40 MB/sec.) Actual transfer rates are somewhat less than this.
Bernoulli box - Removable disk system from Iomega using a SCSI interface and floppy-disk-like cartridges.
Bezel - Also known as the faceplate. A plastic panel that covers the face of a product.
Bit - Stands for "binary digit", the smallest unit of data, represented by a series of "0" and/or "1"
Bit error rate - The ratio of defective bits over total bits on disk¹s surface
Block - An amount of data moved as a single unit; smallest amount of data that can be read or written at a time.
Blocking vs. Non-Blocking - In a blocking architecture the switch can be a bottleneck. Frames of data from a particular port may be held up because the switches internal resources are currently being used (possibly by another port). In a non-blocking architecture the switch will not be a bottleneck. It has sufficient internal resources to handle maximum transfer rates from all ports simultaneously.
Boot drive - A disk drive that contains the operating system
Bps - Bits per second. A measurement of data transmission speed.
Bubble memory - Rugged, solid state magnetic storage device that holds data without power. Globular shaped bubbles (bits) are produced electro-mechanically in circular strings inside a thin-film magnetic recording layer; to read or write the bubbles, they are rotated past a read/write head.
Buffer - Allocated memory space used for temporary storage
Bus - A collection of unbroken signal lines that interconnect computer modules; signal path shared by several devices
Byte - Unit of digital data comprising eight bits, sometimes referred to as a "character." Computer storage devices such as disk drives and memory usually measure their capacity by the number of bytes they can store. A more easily used unit of measure based on bytes is Megabyte.
 

C
Cache memory - A fast, random-access system for storing frequently accessed data in RAM
Channel - General term for a path on which electronic signals travel
Clustering - Clustering is the process of connecting multiple servers together in order to provide greater overall system availability, performance, and capacity for your server platforms. Clustering using MSCS (Microsoft Cluster Server) to connect two servers together provides failover capability, which ensures availability of the server/application. The PowerVault SAN supports multiple clusters to share the same PowerVault 650F.
Coercivity - The strength of the magnetic field required to reverse the polarity of bits
Cold swap - System must be shut down and power turned off before replacing a drive in an array
Compression - Software or hardware process that shrinks data files so that they occupy less storage space, and can be transmitted faster and easier.
Consolidated Storage - Consolidated storage connects multiple servers and/or workstations to a centralized array of hard disk drives. This type of storage setup results in higher availability, manageability, scalability and performance for the applications these servers support. Dell offers two consolidated storage solutions - storage area network (SAN) and network attached storage (NAS).
Controller - A functional unit in a data processing system that controls one or more units of peripheral equipment.
Control Software - 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. (Provided by SNIA)
Control track - Track used for pre-recording media parameters and formal information necessary for writing and reading disk.
CPU- Central Processing Unit.
Cross talk level - The ratio of the level of a spurious signal generated by an adjacent track to the level of the signal of that adjacent track
Curie point - The temperature at which the coercivity of magnetic material declines sharply, allowing a change in orientation by a weaker magnetic field
Cylinder - Aggregate of all tracks that reside in the same location on every disk surface
 

D
DAE - Disk Array Enclosure. Also known as the Dell PowerVault 630F Disk Array Enclosure storage system. The DAE is a JBOD (Just a Bunch Of Disk) enclosure without a storage processor (SP). The DAE supports up to 10 Fibre Channel drives per enclosure and is connected by dual Fibre Channel loops into the DPE. The DPE and 11 DAEs support up to 120 disk modules in a single disk array storage system.
DAT - Digital audio tape. A tape technology designed for very-high quality audio recording and data backup. With their 12GB native capacity, DAT data cartridges are most often used for backing up small servers.
Data Compression - A technique that allows more data to be stored on a given tape. Most manufacturers assume a 2 to 1 data compression can be achieved (i.e. 2 MB of data on 1 MB of tape), but actual results depend on the data being stored.
Data cartridge - Removable magnetic tape module driven by a wheel inside the drive that presses against passive roller in the cartridge
Data library - Data-center housing off-line disks and tapes
Data transfer - The rate at which data is transferred to or from a storage device, expressed in KB/s or MB/s
Decompression - Reverse of compression (see above).
Disaster Recovery - Preventative measures including fault tolerant systems, redundant hardware, and specialized software to ensure that businesses can operate during certain failures, and quickly recover data, hardware and communications assets.
Disk - A round, flat medium with one or more layers deposited on the surface on which data can be recorded
Disk array - Combining redundant disk drives for more capacity, speed, or for disaster recovery
Disk cartridge - A removable disk module containing a single hard disk platter or a floppy disk
Disk drive - A recording or playback device which rotates a disk and records data onto it or retrieves data from it
Diskette - Floppy disk
Disk mirroring - A fault-tolerant technique that writes data simultaneously to two disks using the same disk controller
Disk, optical - A disk containing data in the form of marks in the recording layer that can be read with an optical beam
Disk sector - Magnetic disks are typically divided into tracks, each of which contains a number of sectors; a sector contains a predetermined amount of data, such as 512 bytes
Disk server - A mass storage device that can be accessed by several computers, usually via a local area network
Disk striping - Spreading data over multiple disks drives.
Distributed Storage - Distributed storage is set up so that each server has its own external storage subsystem.
DLT - Digital Linear Tape (1/2" streaming tape)
Domain - A small area which possesses strong magnetization.
DPE - Disk Processor Enclosure. Also known as the Dell PowerVault 650F Disk Array Processor Enclosure storage system. The DPE is an intelligent, highly available, high performance, high capacity disk-array storage system that uses a Fibre Channel Arbitrated Loop (FC-AL) interface. The DPE contains up to 2 Storage Processors (SP) (RAID Controllers). Its modular, scalable design make expansion easy when storage needs increase. The PowerVault 650F or DPE can support up to 11 PowerVault 630F Disk Array Enclosures (DAE) storage systems.
[

E
8mm Tape - A format (named for the width of the tape) first introduced by Exabyte Corp. in 1987, using a helical scan technique that put 2.5GB of storage on one cartridge. Since then, Exabyte has expanded the line to include cartridges and drives with capacities up to 40GB.
Enhanced IDE - Hard disk interface that provides data transfer up to 13 MB/s
Erasable - A disk that can be rewritten
Erase head - Device in magnetic tape drive that erases the tape before a new block of data is recorded
Error correcting code - An error detecting code designed to correct certain kinds of errors in data
Error rate - The ratio of the number of data units in error to the total number of data units
Ethernet - A common method of connecting computers in a LAN. Ethernet transfers data much faster than a dial-up connection--10 million bps
Exclusive OR - A process based on a mathematical algorithm that is used by RAID levels 2-5 to compare data created by a read request during a drive failure or by a write request.
EXTERNAL RAID CONTROLLERS - RAID controllers that reside external to the server, usually in the same enclosure with external disk drives. External RAID controllers communicate with servers via Host Bus Adapters. The advantage of external RAID controllers is that even if a server goes off-line, the user's data is still available.
External storage - Storage of data outside of the CPU, such as disk or tape

F
Failover - The automatic substitution of a functionally equivalent system component for a failed one. The term failover is most often applied to intelligent controllers connected to the same storage devices and host computers. If one of the controllers fails, failover occurs, and the survivor takes over its I/O load. (Provided by SNIA)
FAQ - Frequently Asked Questions. These are files which are maintained by people so that those who are starting out have a rich source of information on the subject in which they are interested. Originally referring a list of questions and answers aimed at new users of a Usenet newsgroup, FAQs are also employed on the Web to convey information quickly and concisely. It is considered good netiquette to read the relevant FAQs on a subject before posting questions in a newsgroup.
Fast SCSI - Synchronous transmission rate defined in SCSI-2 to be used between 5 MHz and 10MHz
Fault tolerance - Redundant components in storage system provide security against system failure
Ferric oxide - An oxidation of iron (Fe2O3) used to coat magnetic disks
Fiber channel - Type of transmission path used as an internal computer channel or network medium; it works with existing interfaces. It transfers data at a rate up to 1 GB per second.
File - All the data that describes one document or image
Firewall - A gateway which protects an organisation's internal Local Area Network (LAN) from external access and tampering from a Wide Area Network (WAN), such as the Internet. Many firewalls disable the functionality of real-time audio and video players such as RealAudio.
Firmware - Low-level software for booting and operating an intelligent device. Firmware generally resides in read-only memory (ROM) on the device. Many read-only memories can be overwritten or programmed using special software. These are called programmable read-only memories, or PROMs. (Provided by SNIA)
Flash disk - Solid state disk made of flash memory
Flash memory - A memory chip that holds data without power, but must be erased in fixed blocks rather than single bytes
Floppy disk - Reusable magnetic storage medium
Format - Arrangement of data in or on medium
Formatting - Process of preparing media to accept data by setting up logical structure of data blocks
Frame - An indivisible unit for transfer of data in fiber channel
Ftpi - flux transitions per inch (tape density)

G
Gigabyte (GB) - A measure of data storage, equivalent to 1,000 megabytes (MB), or approximately 1 billion bytes of data.
Grooved disk - A disk with either surface relief features within the optical depth of focus of the recording layer or reflectivity changes placed within the recording layer along the tracks to provide positional feedback to the radial tracking zone

H
Hard disk - Primary computer storage medium, comprising one or more aluminum or glass platters coated with a ferromagnetic material
Hard error - An error which is uncorrectable by a given error detection and correction system
Hardware - The physical components of a computer, such as the monitor, CPU, keyboard, disk drives, etc.
Head - The device which comes in contact with or comes very close to the magnetic medium
Head crash - Destruction of the hard disk
Head skew - Offset distance from the start of previous track so that the head has time to switch from top of platter to bottom of platter and be a start of new track
Helical recording - A way to write information to a tape that involves spinning the writing head in the reverse direction to the tape movement. Helical scan drives can hold more information on a given tape length than a standard recording head. VCRs are a common example of helical recording.
Helical scan - Recording method used on digital audio tape that runs the tracks diagonally across tape to increase storage capacity.
Hierarchical Storage Management (HSM) - The automated migration of data objects among storage devices, usually based on inactivity. Abbreviated HSM. Hierarchical storage management is based on the concept of a cost-performance storage hierarchy. By accepting lower access performance (higher access times), one can store objects less expensively. By automatically moving less frequently accessed objects to lower levels in the hierarchy, higher cost storage is freed for more active objects, and a better overall cost: performance ratio is achieved. (Provided by SNIA)
Host adapter - Circuitry that translates between a processor¹s internal bus and a different bus, such as SCSI
Hot spare - RAID storage feature that allows a spare drive to be configured on-line for automatic reconstruction in the event of a disk failure.
Hot Spare - This refers to a drive in a RAID configuration that sits idle until one of the RAIDed drives fail. The hot spare then assumes the role of the dead drive. When the dead drive is replaced, you can make it the hot spare.
Hot swapping - Replacing one member disk in a RAID while the RAID is still operating
HSM - Hierarchical Storage Management. A software and hardware system that automatically moves files from hard disks to slower, less expensive storage media (optical and tape).
Hub - The central feature on the disk which interacts with the spindle of the disk drive to provide radial centering and clamping force and, in some cases, axial location

I
I/O - Refers to data that is being sent from the CPU to any type of storage device or peripheral.
Incremental Backup - A backup method which only saves the files within a system that have changed since the last backup. Incremental backups require much less storage space, but take longer to restore after a crash or disaster. Many businesses conduct full backups each week, while conducting the quicker incremental backups each day.
Interface - A set of protocols between components, such as cables and connectors.
IOPS - Input/Output operations per second.
ISO format A - Provisions within ISO 10089 standard which specify the use of a spiral tracking groove in media substrate to maintain head alignment to data track

J
JBOD - Just a Bunch of Disks - refers to drives that reside in their own enclosure external to the server, but contain no RAID intelligence. JBOD drives are dependent on the server for RAID functionality.
Jukebox - A computer-controlled device that stores optical disks and automatically selects, inserts, and ejects disks from drives. Typically it holds five to several hundred optical disks and functions with one or more drives to provide a means to access multi-volume libraries or recorded data
 

K
Kerr effect - Phase-change exhibited by certain materials when exposed to magnetic field
 

L
LAN - Local Area Network. A computer network limited usually to a single physical location such as a floor of a building. See WAN.
Land & groove - A trench-like feature of a disk used to define track locations and applied before recording of any data.
Landing zone - A safe non-data area on a hard disk for parking read/write head.
Laser - A device that produces an intense beam of coherent light. Laser beam reads and writes to optical media. (Acronym for Light Amplification of Stimulated Emission of Radiation).
Laser diode - A laser in which stimulated emission of coherent light occurs at a P-N junction when electrons and holes are driven into the junction by carrier injection, optical excitation, or other means.
Latency - Synonym for I/O request execution time, the time between the making of an I/O request and completion of the request's execution. Also, short for rotational latency, the time between the completion of a seek and the instant of arrival of the first block of data to be transferred at the disk's read/write head. (Provided by SNIA).
Link - One inbound fiber and one outbound fiber connected to a port.
Link Controller Cards - A termination card that handles the logical and physical control of the Fibre Channel link for each mode of use.
Logical Volume - A virtual disk made up of logical disks. Also called a virtual disk, volume set, or partition.
LUN- A LUN (logical unit number) is a logical representation of physical storage. Users can determine whether a LUN is a disk drive, a number of disk drives, or a partition on a disk drive, depending on RAID configuration.
 

M
Magneto - optic-Technology which combines laser and magnetic methods to read and write from a disk
Magnetic disk - Primary computer storage device
Magnetic recording - A technique of recording analog or digital signals or data on a medium of specially prepared grains of iron oxide
Magnetoresistive (MR) - A technology used for the read element of a read/write on hard disk drives; MR means that the resistance to electricity changes in a material when brought in contact with a magnetic field
Mailing List - A distribution list sent to list subscribers. LISTSERV is an automated distribution program for mailing lists.
MBPS- Megabytes per second.
Media - Materials that store data
Megabyte (MB) - Short for 1,048,576 bytes.
Member disk - Any one drive that is part of a RAID sub-system
Mirroring - Also known as RAID 1. Full redundancy is obtained by duplicating all data from a primary disk on a secondary disk.
Mission Critical - Applications that are vital to a company or organization's well being.
MTBF - Mean time between failure

 

N
NAS - Network-attached storage. A general term for stand-alone storage devices connected directly to a local area network. These devices typically don't contain the full network operating system found in a file server, but use a microkernal OS designed to handle specific data read and write functions for a variety of operating systems.
Native Capacity - The storage capacity of a drive when no compression techniques are used. Comparing drives based on their native capacity eliminates differences in manufacturer assumptions concerning file compression.
Network - An arrangement of nodes and connecting branches
Node - A device that has at least one N_port or NL_port
 

O
Optical disk - A direct access disk written or read by light
 

P
Parity - An extra bit, added to a number, used for checking the accuracy of binary numbers.
Partition - A partition is a section of a hard drive. You must create at least one partition to begin using a new hard drive. You can create multiple partitions to keep chunks of data separate. It is also possible to install multiple operating systems on different partitions.
Peripheral - A device that can be attached to a host computer, i.e., with a SCSI bus.
Petabyte (PB) - A unit of measure consisting of one quadrillion bytes (1,000 terabytes).
Phase change - Phase-change technology uses an amorphous coating in which individual spots on the disk are changed by laser irradiation from a crystalline state, which reflects light, to a non-crystalline state, which absorbs light
Platter - A large, round disk for storing data.
Point-In-Time Copy (Instant Snapshot) - The snapshot feature allows users to create an instantaneous virtual image of an existing LUN's data in real-time, which can be viewed and used in the same way as any other LUN. Rather than mirror the data in its entirety, snapshot takes a "picture" of the file pointers that represent the data to be backed up and copies the pointer to another location. Because the file pointers take up so much less space than the actual data, the copy process can be up to ten times faster. The snapshot is kept current via a copy-on-write process from the original LUN.
Preformatted disk - A disk that contains reference data placed and/or written on the disk prior to writing data. The reference data, in the form of grooves or reflectivity changes, provide the disk drive with information that may include sector address, track address, and data synchronization
Protective layer - A transparent layer on the disk provided for mechanical protection of the recording layer, through which the optical beam accesses the recording layer

Q
QIC - Quarter Inch Cartridge. Noted for its low cost, QIC now comes in different cartridge sizes with a various combination of wider and longer tapes. The most common QIC tape today is Travan.
Queue Depth - Specifies the maximum number of outstanding I/Os per disk the selected workers will attempt to activate at one time. For example, if you have 4 disks per LUN in your configuration and specify a queue depth of 16, then the system as a whole will have a maximum of 64 outstanding I/Os at a time (4 disks * 16 outstanding I/Os per disk).

R
RAID - Redundant Array of Independent Disks. RAID hard disk systems use software or firmware to split data across several drives to increase performance and data redundancy. Different RAID levels organize the data across the drives in different ways.
Raid Controllers - RAID controllers are I/O devices that control the layout and format of the data. A RAID controller places data across multiple media or device type according to the RAID group specified.
RAIL - RAIL stands for RAID on Library. Library in this case refers to tape library. RAIL refers to creating a RAID type with entire tape libraries. RAID is a term that can be applied to disk, tape or optical media types or devices.
RAIT - RAIT stands for RAID on Tape. RAID is a term that can be applied to disk, tape or optical media types or devices. To distinguish tape technology from disk or optical technology the industry has adopted the term RAIT to represent RAID on tape.
Read error - Failure to read data on a storage device
Read-only - Storage media that permanently stores data
Read power - The incident radiant power specified at the entrance surface to read data from disk without damaging recording layer
Read/write - File that can be updated and erased
Read/write head - A device that reads and writes data on a magnetic disk or tape
Recording density - The number of bits in a single linear track measured per unit length
Recording layer - A layer of the disk on or in which data is written during manufacture, use or both.
Redundant - In a redundant system, if you lose part of the system, it can continue to operate. For example, if you have two power supplies with one that takes over if the other one dies, that's redundancy.
Reed-Solomon code - An error detection code or an error correcting code or a combination of both which is particularly suited to the correction of burst errors or errors that are strongly correlated
Reflectivity - Ratio of incident light to reflected light measured at normal incidence on disk at a specified wavelength
Rewritable - Rewritable drives can erase recorded data and rewrite an update file in its original sector location

S
SAN - Storage area network. A new architecture for a pool of centralized storage. A SAN usually includes multiple servers working off a centralized data store made up of highly reliable and redundant hardware, including RAID. The object is to provide a single point of storage with sophisticated management. Fibre channel is an important part of the SAN concept, because it works with existing data storage technologies, including SCSI and network connections.
Scale/Scalable/Scalability - In computer systems, to grow or support growth in such a way that all capabilities of the system remain in constant ratio to each other. For example, a storage subsystem whose data transfer capacity increases by the addition of buses as its storage capacity increases by the addition of disks is said to be scalable. (Provided by SNIA)
SCSI - Small computer system interface. A hardware peripheral interface used most often with storage devices such as disks, CD-ROM and tape drives. SCSI comes in several incarnations which can move data at rates ranging from 5 to 40MBps. You can connect more than one SCSI controller to a SCSI cable for increased reliability.
Sector - A triangular section of a disk surface; a block of data is addressed by its track and sector numbers
Sector ID - Data encoded in sector header that provides a means of identity
Seek time - The time to position the read/write head to a specified track location on the disk, not including head setting time
Serial interface - Data communications mode in which bits are sent in sequence; contrast with parallel interface
Server - Software (or a hardware and software combination) which provides a specific kind of service and information to client software which may run on other computers. For example, Web servers allows one to access the Web documents located on them.
Signal-to-noise ratio - An amplitude measurement; the ratio of system noise to the maximum information level within a given signal, usually expressed in dB
Soft error - An error which is correctable by an error detection and correction system
Spindle - The part of the disk drive that contacts the disk and/or the hub
Spindle clamp - The part of the disk drive responsible for providing the hold-down force that prevents the disk from slipping when the spindle is accelerated and also provides the centering force when the disk is loaded onto the spindle
Spot size - The 1/e2 beam diameter or full-width/half-maximum beam diameter of laser at recording layer.
Storage Controller - An intelligent controller to which storage devices are attached. (Provided by SNIA).
Striping - Spreading data evenly over multiple disk drives to enhance performance
Substrate - Rigid material supporting the recording medium

T
Tape drive - The machine that transports, reads, and/or writes a magnetic tape.
Terabyte (TB) - A unit of measure consisting of one trillion bytes (1,000 gigabytes).
Thin film - A microscopically thin layer of semiconductor or magnetic material that is deposited onto a metal, ceramic, or semiconductor base
Thin-film head - A read/write head made from thin layers of a conducting film deposited onto a nickel-iron core
Track - Path or sets of paths on medium associated with a single reading or writing head as medium moves past head; for an optical disk, a 360 degree segment of path which is to be followed by read beam during reading or write beam during writing
Transfer rate - The rate at which bytes or bits are transferred, usually expressed as MB/s
Travan - A tape technology that evolved out of the industry-standard QIC. Travan delivers more capacity than previous QIC formats. With capacities ranging from 400MB to 20GB, Travan formats are best for backing up individual machines or small servers.

V
Virtual Devices - A device presented to an operating environment by control software or by a volume manager. From an application standpoint, a virtual device is equivalent to a physical one. In some implementations, virtual devices may differ from physical ones at the operating system level (e.g., booting from a host based disk array may not be possible). (Provided by SNIA).
Virtual Disks - A set of disk blocks presented to an operating environment as a range of consecutively numbered logical blocks with disk-like storage and I/O semantics. The virtual disk is the disk array object that most closely resembles a physical disk from the operating environment's viewpoint. (Provided by SNIA).
Volume - A volume is a unit of storage within which space can be allocated by a storage manager and accessed via a single file system. Historically, a volume has corresponded to a physical unit, but it has recently been used for a collection of physical units with a single external address (for example, a RAID array) or for a subset (partition) of a physical unit. Typically a volume contains data sets or data base records.