[Network] Acronym for Wide Area Network.
[Computer System] The substitution of a replacement unit (RU) in a system for a defective one, where in order to perform the substitution, the system must be stopped (causing it to cease performing its function), but power need not be removed.
[Network] The splitting of light into a series of “colors” from a few (sparse WDM) to many with a narrow wavelength separation (dense WDM) for the purpose of carrying simultaneous traffic over the same physical fiber (9 micron usually).
Each “color” carries a separate data stream.
[Management] Acronym for Web Based Enterprise Management.
1. [Network] Acronym for Wave Division Multiplexing.
2. [Windows] Acronym for Windows Driver Model.
[Storage System] A set of algorithms utilized by a flash controller to distribute writes and erases across the cells in a flash device.
Cells in flash devices have a limited ability to survive write cycles. The purpose of wear leveling is to delay cell wear out and prolong the useful life of the overall flash device.
[Management] An initiative in the DMTF, comprising a set of technologies that enable interoperable management of an enterprise.
WBEM consists of CIM, an XML DTD defining the tags (XML encodings) to describe the CIM Schema and its data, and a set of HTTP operations for exchanging the XML-based information. CIM joins the XML data description language and HTTP transport protocol with an underlying information model (the CIM schema) to create a conceptual view of the enterprise.
The service may be distributed in many elements throughout the fabric or it may be centralized in one or a few elements. A well-known address is not subject to zone restrictions; i.e., a well-known address is always accessible, irrespective of the current active zone set.
[Network] A communications network that is geographically dispersed and that includes telecommunications links.
[SCSI] Any form of SCSI using a 16-bit data path.
In a wide SCSI implementation, the data transfer rate in MBytes per second is twice the number of megatransfers per second because each transfer cycle transfers two bytes. See fast SCSI, Ultra SCSI, Ultra2 SCSI, Ultra3 SCSI.
[Windows] A facility of the Windows operating system that translates between IP addresses and symbolic names for network nodes and resources.
[Windows] The Microsoft framework that supports CIM and WBEM; a set of Windows operating system facilities that enable operating system components to provide management information to management agents.
[Windows] Acronym for Windows Internet Naming Service.
[Windows] Acronym for Windows Management Instrumentation.
1. [General] An addressable unit of data in computer memory.
The length is specified by the computer architecture and is typically 8,16, 32, or 64 bits. Most processor architectures include arithmetic and logical instructions that operate on words.
2. [Fibre Channel] The smallest Fibre Channel data element consisting of 40 serial bits representing either a flag (K28.5) plus three encoded data bytes (ten encoded bits each) or four ten bit encoded data bytes.
3. [Fibre Channel] A string of four contiguous bytes occurring on boundaries that are zero modulo four from a specified reference. See transmission word.
[Computer System] A group of UNIX or Windows computer system users and/or computers, usually with a common mission or project, that is created for administrative simplicity.
[Fibre Channel] A Node_Name that is worldwide unique
[Fibre Channel] A Port_Name that is worldwide unique.
[Fibre Channel] A Name_Identifier that is worldwide unique, and represented by a 64-bit value.
[Storage System] Acronym for Write Once Read Many.
[Data Security] An independent program that replicates from computer to computer across network connections, often clogging networks and computer systems as it spreads.
Write-back cache includes an inherent risk that an application will take some action predicated on the write completion signal, and a system failure before the data is written to non-volatile media will cause media contents to be inconsistent with that subsequent action. For this reason, good write-back cache implementations include mechanisms to preserve cache contents across system failures (including power failures) and to flush the cache at system restart time. See write through cache.
[Storage System] The process of accumulating the data for a number of sequential write requests in a cache, and performing a smaller number of larger write requests to achieve more efficient device utilization.
[Storage System] A potential data corruption problem for parity RAID technology resulting from an array failure while application I/O is outstanding, followed by an unrelated member disk failure (some time after the array has been returned to service).
Data corruption can occur if member data and parity become inconsistent due to the array failure, resulting in a false regeneration when data from the failed member disk is subsequently requested by an application. Parity RAID implementations typically include mechanisms to eliminate the possibility of write holes.
[Storage System] A type of storage, designed for fixed content, that preserves what is written to it in an immutable fashion.
Optical disks are an example of WORM storage.
[Storage System] Low apparent application write performance to RAID arrays’ virtual disks.
The write penalty is inherent in RAID data protection techniques, which require multiple disk I/O requests for each application write request, and ranges from minimal (mirrored arrays) to substantial (RAID Levels 5 and 6). Many RAID array designs include features such as write-back cache specifically to minimize the write penalty.
[Computer System] A caching technique in which the completion of a write request is not signaled until data is safely stored on non-volatile media.
Write performance with a write-through cache is approximately that of a non-cached system, but if the data written is also held in cache, subsequent read performance may be dramatically improved. See write back cache.