A glossary of storage networking, data, and information management terminology
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About the SNIA Dictionary
by the Storage Networking Industry Association
The SNIA Dictionary contains terms and definitions related to storage and other information technologies, and is the storage networking industry's most comprehensive attempt to date to arrive at a common body of terminology for the technologies it represents. The terms go through a rigorous technical review and approval process by the SNIA Technical Council to assure their accuracy. The SNIA Technical Council is a group of industry technical experts elected by the members of the SNIA to guide the SNIA’s technical efforts. Their extensive individual technical backgrounds cover all aspects of storage.
The reader should recognize that in this rapidly evolving field, new terminology is constantly being introduced, and common usage is shifting. The SNIA regards this dictionary as a living document, to be updated as necessary to reflect a consensus on common usage, and encourages readers to treat it in that spirit. Comments and suggestions for improvement are gratefully accepted at any time, with the understanding that any submitter of comments or suggestions contributes them to SNIA; and SNIA will therefore own the rights to them. Comments and suggestions may be directed to email@example.com.
Proposals for new terms or definitions, or modifications to existing ones, should be submitted on the form located at: http://www.snia.org/education/dictionary/submittal
Currently the dictionary is published online and in PDF format approximately every six months--in spring and fall. A paper version is published, with sponsorship opportunities, each spring.
Download the 2014 SNIA Dictionary (4 MB, updated September 12, 2014)
The SNIA hereby grants permission for individuals to use this glossary for personal use only, and for corporations and other business entities to use this glossary for internal use only (including internal copying, distribution, and display), provided that:
Any definition reproduced must be reproduced in its entirety with no alteration, and, any document, printed or electronic, in which material from this glossary (or any portion hereof) is reproduced must acknowledge the SNIA copyright on that material, and must credit the SNIA for granting permission for its reuse.
Other than as explicitly provided above, you may not make any commercial use of this glossary, sell any or all of this glossary, or distribute this glossary to third parties. All rights not explicitly granted above are expressly reserved to SNIA. In particular, the provisions above do not grant the rights to make any commercial use of this glossary, sell any or all of this dictionary, or distribute this dictionary to third parties.
Permission to use this glossary for purposes other than those enumerated above may be requested by e-mailing firstname.lastname@example.org; please include the identity of the requesting individual and/or company and a brief description of the purpose, nature, and scope of the requested use.
Copyright © 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014 Storage Networking Industry Association, All Rights Reserved. Last updated April 22, 2014.
The format for definitions has changed as of the last half of 2008. Terms are now defined as much as possible using the substitution principle, which states that a term's definition should be substitutable for the term itself in a sentence.
In the case that more text is required or deemed helpful, it is contained in one or more separate paragraphs after the definition itself. This text is informative in nature, and while intended to be accurate, is not technically part of the definition itself.
In many cases, as technology develops, companies are forced to invent new terminology to describe innovations in their products. As the technology matures and vendors attempt to compete and compare their products with others, one or two terms become the most widely used, yet a number of other terms may remain in some use which are basically synonyms for the widely used terms. This causes confusion in the marketplace. To encourage crispness and uniformity in product descriptions, this dictionary lists synonyms of this type as "Deprecated synonym for xxxx," where xxxx is the term determined to have become canonical in the industry. This is to indicate both the meaning of xxxx and guide the reader toward use of the more canonical term.
In cases where a synonym is not deprecated, the SNIA does not endorse the use of one synonym over another.
Definitions taken from standards documents
The SNIA has a strong interest in keeping definitions harmonized across various industry groups and national and international standards bodies. Towards this end, some definitions, especially those pertaining to Fibre Channel and SCSI terms and technologies, have been quoted from the appropriate version of the INCITS standard. In all such cases, the INCITS standard is authoritative. The SNIA dictionary may include terms defined in the the following standards and draft standards:
INCITS 302-1998, SCSI Parallel Interface - 2 (SPI-2)
INCITS 367-2003, SCSI Parallel Interface - 5 (SPI-5)
INCITS 405-2005, SCSI Block Commands - 2 (SBC-2)
INCITS 431-2007, Serial Attached SCSI - 2.1 (SAS-2.1)
INCITS 447-2008, SCSI Architecture Model - 4 (SAM-4)
INCITS 448-2008, SCSI Enclosure Services - 2 (SES-2)
INCITS 461-2010, Fibre Channel - Switch Fabric-5 (FC-SW-5)
INCITS 462-2010, Fibre Channel - Backbone-5 (FC-BB-5)
INCITS 466-2011, Fibre Channel - Single-Byte Command Code Sets - 4 (FC-SB-4)
INCITS 467-2011, SCSI Stream Commands - 3 (SSC-3)
INCITS 470-2011, Fibre Channel - Framing and Signaling - 3 (FC-FS-3)
INCITS 475-2011, Fibre Channel - Inter-Fabric Routing (FC-IFR)
INCITS 476-2011, SAS Protocol Layer (SPL)
INCITS 476/AM1-2012, SAS Protocol Layer Amendment #1 (SPL-AM1)
INCITS 477-2011, Fibre Channel – Link Service - 2 (FC-LS-2)
INCITS 478/AM1-2014, Serial Attach SCSI - 2.1 Amendment #1 (SAS-2.1-AM1)
INCITS 479-2011, Fibre Channel - Physical Interface - 5 (FC-PI-5)
INCITS 481-2012, Fibre Channel Protocol for SCSI - 4 (FCP-4)
INCITS 484-2012, SCSI Media Changer Commands - 3 (SMC-3)
INCITS 497-2013, Automation/Drive Interface – Commands - 3 (ADC-3)
INCITS 505-2013, SAS Protocol Layer - 2 (SPL-2)
INCITS 509-2014, Fibre Channel - Backbone - 6 (FC-BB-6)
INCITS 514-2014, SCSI Block Commands - 3 (SBC-3)
INCITS 516-2014, SCSI Stream Commands - 4 (SSC-4)
INCITS 519-2014, Serial Attached SCSI - 3 (SAS-3)
The SNIA wishes to thank ANSI and INCITS for their cooperation in this matter.
Copies of INCITS standards may be purchased at ANSI's online store at http://webstore.ansi.org.
Most of the terms in this dictionary have meaning primarily in specific sub-contexts of storage networking, such as SCSI or File Systems. The following categories are used to declare the context in which a given definition in this dictionary is held to be valid. No attempt has been made to date to rigorously define these categories, so they remain a guide to understanding, not a formal system.
Long Term Retention
The context hierarchy is a work in progress. In part, we are constrained by practice in previous editions of the dictionary. In the above hierarchy representation, context labels indented beneath other context labels represent specializations of the higher-order label concept. Below is an example of how context is indicated:
[Context] The context is called out in square brackets at the beginning of each definition, as in this example.
The following SNIA volunteers contributed to this version of the SNIA Dictionary:
Alan G. Yoder, Huawei, Lead
Mark Carlson, Toshiba
Leah Shoeb, The Evaluator Group
Past contributors include:
David Black, EMC Corporation
Roger Cummings, Symantec
Eric Hibbard, HDS
Steve Wilson, Brocade
Thanks also to the many unsung contributors who have submitted suggestions through the online submission portal.