valid data byte

[Fibre Channel] A string of eight contiguous bits within FC-P1 that represents a value between 0 and 255.

valid frame

[Fibre Channel] A received frame containing a valid Start of Frame (SOF), a valid End of Frame (EOF), valid data characters, and proper Cyclic Redundancy Check (CRC) of the Frame Header and Data Field.

validity control bit

[Fibre Channel] A control bit that indicates whether a field is valid.

If a validity control bit indicates that a field is invalid, the value in the field is treated as invalid and ignored.

variable-length segmentation

[Storage System] Partitioning a byte stream into parts that are not a constant number of bytes when performing compression or hash-based data deduplication.

See fixed-length segmentation.


[Storage System] Acronym for Virtual Block Address.


[Network] Acronym for Virtual Channel Identifier.


[Fibre Channel] Acronym for Vertical Cavity Surface Emitting Laser.

vendor unique

[Standards] Aspects related to a standard (e.g., functions, codes, etc.) not defined by the standard, but offered by a single vendor within the framework of the standard.

Functionality unique to a given vendor may be exposed using standard methods. For example, many vendors offer vendor-specific SNMP MIBs that users of the SNMP standard can use to obtain system information.


[Data Recovery] The object-by-object comparison of the contents of a backup image with the online data objects from which it was made.


[Data Recovery] The maintenance of multiple point-in-time copies of a collection of data.

Versioning is used to minimize recovery time by increasing the number of intermediate checkpoints from which an application can be restarted.

Vertical Cavity Surface Emitting Laser (VCSEL)

[Fibre Channel] A surface emitting laser source fabricated on a planar wafer with emission perpendicular to the wafer.


[Fibre Channel] [Network] The Name_Identifier of a VE_Port.


[Fibre Channel] Acronym for Virtual Fabric.


[Fibre Channel] Shorthand for Virtual Fabric Identifier.


[Fibre Channel] [Network] The Name_Identifier of a VF_Port.

VFT Tagging E_Port

[Fibre Channel] An E_Port that has enabled processing of Virtual Fabric Tagging Headers.

VFT Tagging F_Port

[Fibre Channel] An F_Port that has enabled processing of Virtual Fabric Tagging Headers.

VFT Tagging PN_Port

[Fibre Channel] A PN_Port that has enabled processing of Virtual Fabric Tagging Headers.


[Fibre Channel] Short for Virtual Fabric Tagging Header.


[Computer System] Acronym for Virtual Interface Architecture.

virtual block

[Storage System] A block in the address space presented by a virtual disk.

Virtual blocks are the atomic units in which a virtual disk’s storage capacity is typically presented by RAID arrays to their operating environments.

virtual block address

[Storage System] The address of a virtual block.

Virtual block addresses are typically used in hosts’ I/O commands addressed to the virtual disks instantiated by RAID arrays. SCSI disk commands addressed to RAID arrays are actually using virtual block addresses in their logical block address fields.

Virtual Channel Identifier (VCI)

[Network] A unique numerical tag contained in an ATM cell header.

A VCI identifies an ATM virtual channel over which the cell containing it is to travel.

virtual device

[Storage System] 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.

virtual disk

[Storage System] 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. See logical disk.

Virtual E_Port (VE_Port)

[Fibre Channel] [Network] The data forwarding component of an FC Entity that emulates an E_Port and is dynamically instantiated on successful completion of an ELP Exchange.

The term virtual indicates the use of a non Fibre Channel link connecting the VE_Ports.

Virtual F_Port (VF_Port)

[Fibre Channel] [Network] The data forwarding component of an FC Entity that emulates an F_Port and is dynamically instantiated on successful completion of an FLOGI Exchange.

The term virtual indicates the use of a non Fibre Channel link connecting a VF_Port with a VN_Port.

Virtual Fabric (VF)

[Fibre Channel] A Fabric identified by a VF_ID composed of partitions of switches and N_Ports having the properties of: 1) a single Fabric management, 2) independence from all other Virtual Fabrics, e.g., an independent address space.

virtual fabric identifier

[Fibre Channel] A value that uniquely identifies a Virtual Fabric among all the Virtual Fabrics that share a set of switches and N_Ports.

Virtual Fabric Tagging Header (VFT_Header)

[Fibre Channel] An Extended_Header that contains information to associate a frame to a specific Virtual Fabric.

Virtual Interface Architecture (VIA)

[Computer System] An API specification for direct communication among distributed applications developed by Intel, Compaq, and Microsoft.

VIA reduces interprocess communication latency by obviating the need for applications to use processor interrupt or operating system paths to intercommunicate, while maintaining security on the communications path. VIA is interconnect neutral. See Fibre Channel Virtual Interface.

Virtual Link

[Fibre Channel] [Network] The logical link connecting two FCoE_LEPs. over a Lossless Ethernet network and is identified by the pair of MAC addresses of the two link end-points.

Virtual Local Area Network (VLAN)

[Network] A logical network that behaves as if it is physically separate from other physical and virtual LANs supported by the same switches and/or routers.

Virtual N_Port (VN_Port)

[Fibre Channel] [Network] The data forwarding component of an FC Entity that emulates an N_Port and is dynamically instantiated on successful completion of an FLOGI or FDISC Exchange.

The term virtual indicates the use of a non Fibre Channel link connecting a VN_Port to a VF_Port.

Virtual Path Identifier (VPI)

[Network] An eight-bit field in an ATM cell header that denotes the cell over which the cell should be routed.

Virtual Switch

[Fibre Channel] A Switching Construct that resides in a Core Switch and corresponds to a Virtual Fabric.

Multiple Virtual Switches may reside within a Core Switch.

virtual tape

[Storage System] A virtual device with the characteristics of a tape.

Virtual Tape Library (VTL)

[Backup] A storage system that emulates a library.

VTLs are usually classified as near-online devices, and provide faster Max TTFD than tape, but normally not as fast as online systems. They typically use slower drives with higher capacities than high-performance systems, and therefore offer a better energy footprint per unit of data.


[Computer System] Software that enable a single hardware platform to support multiple concurrent instances of systems such as storage, networking, or computing facilities.

Examples of virtualization are compute virtualization and storage virtualization.


[Data Security] A type of programmed threat; a code fragment (not an independent program) that replicates by attaching to another program, and either damages information directly or causes denial of service.


[Network] Acronym for Virtual Local Area Network.


[Fibre Channel] Synonym for Nx_Port, used when it is desired to emphasize the support for Virtual Fabrics and/or N_Port Identification Virtualization.


[Fibre Channel] [Network] The Name_Identifier of a VN_Port.

VN_Port MAC address

[Fibre Channel] [Network] The MAC address used by an ENode for a particular address identifier during FC operation using FCoE frames.


[Computer System] Synonym for node, used when it is desired to emphasize the support for multiple nodes within a platform.


[Computer System] A property of data yielding the possibility that it will be obliterated if certain environmental conditions are not met.

For example, data held in DRAM is volatile, since if electrical power to DRAM is cut, the data in it is lost. See non-volatility, persistence.


1. [Storage System] Synonym for virtual disk.

2. [Storage system] A storage element that has been prepared for use.

Examples include Logical Unit, tape cartridge, LTFS Volume, and USB thumb drive.

volume group

[Data Recovery] A collection of removable media that reside in a single location, for example in a single robot or group of interconnected robots.

volume manager

[Storage System] Common term for host-based control software.

volume pool

[Data Recovery] A logical collection of removable media designated for a given purpose, for example, for holding the copies of a single repetitive backup job, or for backing up data from a given client or set of clients.

A volume pool is an administrative entity, whereas a volume group is a physical one.

volume set

[Storage System] Synonym for virtual disk.


[Network] Acronym for Virtual Path Identifier.


[ Fibre Channel] A collection of ports from a set of connected storage networking switches, that form a virtual network.

Ports within a single switch can be partitioned into multiple VSANs, despite sharing hardware resources. Conversely, multiple switches can join a number of ports to form a single VSAN.


[Backup] Acronym for Virtual Tape Library.


[Data Security] A defect in data protection mechanisms that could be exploited by a threat.