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Megabyte's Storage Dictionary

I hope you find this glossary useful. Even I get confused sometimes by the new words that vendors throw at me. There are over 100 storage terms listed below in alphabetical order.

A to Z of SSD
popular SSD articles
History of data storage
flash SSD Jargon Explained
A Storage Architecture Guide
History of Disk to Disk Backup
the Solid State Disks Buyers Guide
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Sometimes Megabyte wasn't sure if he
understood the true meaning of all the
words he was reading.
Phrase or acronym Description Related ORG, articles & info


...later:- became PCIe
The third-generation I/O architecture (code-named 3GIO) will be designed as a highly flexible, reliable, serial I/O architecture that will scale to the theoretical limits of copper. It will comprehend the needs of multiple markets segments such as desktop, mobile, server, communications and embedded applications and remain compatible with the existing PCI programming model. Products based on third-generation I/O architecture are expected to begin emerging in the marketplace in the second half of 2003. Companies working on this standard are known as the "Arapahoe Work Group".

...Later:- this standard was renamed to PCI Express (PCIe)
PCI Special Interest Group, PCIe SSDs

ADC ATA Disk on Chip:- is a chip which includes a solid state disk and an industry standard PC AT (ATAPI) bus interface. .

AIT Advanced Intelligent Tape™ - is a Sony brand of tape cartridge. With a capacity of up to 35GB and a data transfer rate of up to 4MB/sec., Sony's AIT-1 drive offers an ideal entry-point to AIT. The technology will offer up to 100GB per cartridge with AIT-3 starting in the third quarter of 2001, all the way to 800GB per cartridge before the end of the decade.

...from featured press release - April 18, 2001
AIT Forum

Amplification Write Amplification - is a term popularized by SiliconSystems in various flash SSD related articles and press releases.

Gary Drossel, a VP at SiliconSystems defines it as follows. "Write Amplification - is a measure of the efficiency of the SSD controller. Write amplification defines the number of writes the controller makes to the NAND for every write from the host system. Long, continuous writes map over this mismatch, but most embedded/ enterprise applications do not stream data. Instead, they transfer data in a series of shorter, more random transactions."

It's the difference in ratio between the number of theoretical writes you think that your application does to a flash SSD - compared to what actually happens - due to OS or other software - which is often outside your control. Write Amplification can be a serious problem - because it can invalidate calculations related to endurance. SiliconSystems says - the best thing to do is measure it - rather than estimate it. Their SSDs can be used as tools to do this - because they perform real-time internal logs of write cycles.
storage reliability

ASAPs Auto-tuning SSD Accelerated Pools of storage - is a new term (November 2009) coined by to describe a product category which includes products like the following:- Although aimed at different markets, and having different interfaces, what they all have in common is their ability to self-tune.

In effect - "ASAPs eliminate waits for the SSD Hot-Shot / Hot-Spot Engineer ..."

Attenuation Write Attenuation - is a term coined by the editor of It is the opposite effect of Write Amplification - and reduces the amount of writes done to the SSD compared to what you expect. This kind of out-of-sequence recognition, and packetization before writes usually requires a non volatile RAM or similar memory inside the SSD controller. Beneficial side effects of Write Attenuation are:- lower wear-out of the flash SSD. and (often) faster random IOPS - because the nv cache doesn't have to be flushed out as inefficiently - as in the case of unprotected RAM caches. Z's Laws - Predicting Future Flash SSD Performance

AoE ATA-over-Ethernet, is a network storage standard created by Coraid. It provides a simple user interface to mount disks on the network.and is supported by a number of vendors. AoE - resource directory

ATAPI AT Attachment Packet Interface:- the AT part refers to the IBM PC bus used in the 1980's vintage 286 based PC. The Brief History of ATA and ATAPI

ATOMM In 1992 Fujifilm introduced ATOMM (an acronym for Advanced super Thin layer and high Output Metal Media), the metal particle coating technology that promised great leaps in storage capacity, performance and reliability. Within a few short months of ATOMM's announcement, a Fujifilm relationship with Iomega Corporation led to the development of the Zip data storage system, which brought disk capacity from 1.44MB to 100MB and then 250MB, launching the high-capacity floppy disk category.

...from a featured release by Fujifilm

Bit Bit is the smallest amount of information in a binary digital system. It can be used to represent 2 states of information, such as YES or NO. .

Bluefin The SNIA specification, code-named 'Bluefin', employs technology from the Web Based Enterprise Management (WBEM) initiative that uses the Managed Object Format (MOF) to describe system resources based on a Common Information Model (CIM). Bluefin introduces new technology for security, locking, and discovery for SAN management.

...from a press release May 22, 2002, by SNIA
SAN - software

BRM Backup Resource Management

...from a press release (September 24, 2001) by Bocada

Byte A byte is 8 bits of information which is regarded as one word. A byte can represent 256 different states, for example numbers, processor instructions, or a combination of letters and numbers as in the ASCII code. .

CDN Content Delivery Network. Relates to internet based storage services which provide agreed service levels and performance. Storage Services

CE-ATA Consumer Electronics ATA standards group developing an interface for handheld disk market with software compatibility to ATA. Founded Sep 2004. Industry trade associations

CIM Common Information Model

Compliance In the storage context, compliance refers to a whole bundle of legislation, rules and conventions which impact the way that data is stored, archived, retrieved and encrypted.

These are summarised in a practical way in this article:- Privacy and Security Regulations, and How they Impact Storage Systems

Consolidation Storage consolidation is the concept of centralizing and sharing storage resources among numerous application servers. Storage consolidation architectures are designed to address the limitations associated with direct-attached storage (DAS) and solve the growing data demands dictated by information-rich business environments. Storage consolidation history

... from the article - Storage Consolidation - by Datalink

DAFS Direct Access File System (DAFS) protocol. The DAFS protocol is a new file access protocol, specifically designed to take advantage of standard memory-to-memory interconnect technologies such as VI (the Virtual Interface Architecture) and InfiniBand in high-performance clustered data center environments. DAFS enables applications to access network interface hardware without operating system intervention, and carry out bulk data transfers directly to or from application buffers with minimal CPU overhead.

from featured press release - April 4, 2001 - DAFS Collaborative
DAFS Collaborative

Industry trade associations

DAS Directly Attached Storage. In the old days all mass storage devices such as disk drives etc were attached directly to the nearest computer (or were located inside the same box) so there was no need for a term describing this. But since the technologies which enable storage networking have become more prevalent, the term DAS has been used to describe those parts of a wider storage network in which this local connection is still used. .

DAT Digital Audio Tape

DDP Disk-based Data Protection, in which a disk or RAID system is used as a backup system instead of a tape drive or tape library.

DDR Double Data Rate is a memory bus technology used to connect RAM on motherboards.

DICOM Digital Imaging and Communications in Medicine .

DIMM Dual In-line Memory Module

...from a featured release by Kentron Technologies

DLTtape With an installed base of more than 1.7 million DLTtape drives in use today, more than 70 million DLTtape media cartridges, and now tens of thousands of Super DLT drives shipped to date, DLTtape technology is the de facto standard for backup and archiving of business-critical data. The DLTtape logo ensures media compatibility with the installed base. The first of the next generation of Super DLTtape drives is the SDLT 220 drive. It operates at a native capacity of 110 GB and a native transfer rate of 11MB/second, and provides backward read compatibility with millions of DLTtape IV media cartridges recorded on DLT 4000, DLT 7000, DLT 8000, and DLT1 drives. Future generations of Super DLT drives will store more than one terabyte of capacity per data cartridge.

Like previous generations of DLTtape drives, Super DLTtape drives support all major systems and platforms, and all major Independent Software Vendors (ISVs) support the Quantum DLTtape line.

from a featured press release, October 30, 2001 by Quantum

DVD Digital Versatile Discs provide superb video, audio and data storage and access -- all on one disc.

...from article:- DVD FAQs - The DVD Forum
DVD Forum

DVD drives

Endurance Is a term used in the context of flash memory or flash solid state disks and is more verbosely called "Write Endurance."

Simple explanation... The number of write cycles which can be performed by any block of flash is limited due to physics and technology imperfections which eventually make the data storage process unreliable.

That number varies according to the type of flash (MLC is usually 10x worse than SLC) and according to the memory generation and also whether it has been designed (or selected) for high endurance.

Typical quoted values in the market today (2009) range from as low as 100,000 to over 2 million cycles.

Wear leveling and write attenuation are architectural techniques which can be used in SSD controllers to mitigate the effects of endurance - and extend usable life of a memory array by many orders of magnitude compared to the intrnsic life of a dumb flash array without such a controller.
article:- SSD Myths and Legends - "write endurance"

Exabyte Exabyte is a measure of the size of storage. It's equal to

1,024 x 1,024 x 1,024 x Gigabytes = just over 1 billion Gigabytes.

This is not yet a practical unit of storage for most real people, but if information keeps expanding at current rates, we'll start to get more familiar with it towards the end of the first decade of the 21st century.

Exabyte is also the name of a tape drive company founded in 1985.
article:- "How Much Information?"

Fabless If you're unfamiliar with the term "fabless" - when it's used by a semiconductor company - it means that the company doesn't have its own wafer fabrication plant, but designs chips which will be manufactured using the production capacity of a 3rd party company. The term "wafer" - is because hundreds of integrated circuits are produced on a slice of silicon which in the old days used to be the shape and size of a (Catholic) communion wafer but wafers have now expanded to the diameter and appearance of a 12 inch CD. After adding layers of toppings, cooking and processing - the wafer is cut into individual chips. We used the pizza metaphor on our storage chips page - because there is some similarity with that industry. But Pizza tastes better and modern wafer fabs, can cost billions of dollars to build and commission. chips

Fabric In the context of a storage area network, the fabric, refers to the detailed make up of the network such as cards and attached devices. Fibre channel switches & hubs

FAS Fabric Attached Storage conveniently bundles together the ideas of SAN and NAS, or Networked Storage

...from a July 2002 document by EMC and Gartner

Fat flash SSD Classification defined in the article RAM Cache Ratios in flash SSDs. A flash SSD in which the ratio of RAM cache to flash array is at least 10x higher than that in (more common) regular flash SSDs.

FB-DIMM Fully Buffered Dual In-line Memory Module. The FB-DIMM architecture overcomes the previous limitation of two-to-four module capacity per channel. A FB-DIMM system's DRAM module content can be increased to as many as eight modules without reducing the speed.

...from a December 2005 release by Samsung Electronics

FCI Flux Changes per Inch - is a term related to magnetic disk drives. It's not a parameter which is relevant to most users. But when a computer manufacturer is evaluating what disks to buy, that figure tells them something about which generation of magnetic media is being used, in a similar way to the geometry figures you sometimes see quoted by semiconductor manufacturers. Hard drives

FCIP Fibre Channel over IP Fibre channel routers


FCoE Fibre Channel over Ethernet First products came to market in October 2007.

FEMMA™ technology FEMMA™ (Foldable Electronic Memory Module Assembly) was designed by memory manufacturer Kentron Technologies to be utilized in the "1U", "blade" and "hyper dense" server platform environments and telecom markets where space and height constraints are at a minimum. Kentron's low profile FEMMA based memory modules have been widely accepted by system developers for their advanced thermal properties, high density, and leading price/performance position. FEMMA technology is scalable to future chip technologies such as BGA (Ball Grid Array) and Flash. RAM

Fibre-Channel Fibre-Channel is an interface standard for connecting computers to mass storage devices such as disk drives and tape libraries. Developed more than a decade after SCSI, which it was intended to replace for high performance applications, the Fibre-Channel standard was specified around faster data throughput speeds, and longer distances because of its use of fiber-optic cable. The differences in spelling were done deliberately by the standard creators. In the meantime, new versions of SCSI have caught up in speed terms, so the performance differences are now blurred. FibreAlliance

Fibre Channel Industry Association

Fibre-channel adapter cards, Fibre channel cables, Fibre channel routers, Fibre channel switches & hubs

FICON IBM Mainframe Fiber Optic Connection. FICON maps ESCON over Fibre Channel for links much longer than standard Fibre Channel, creating a special requirement for extended credit buffers. QLogic's QLA2300 Series HBAs can connect FICON at distances of up to 500 kilometers.

...from a featured press release about QLogic
ESCON interfaces

Garbage Collection Garbage Collection is an important background process in flash SSD controllers. Some editors and software vendors (who don't understand flash technology) mistakenly attribute a long term slow down in some SSDs to fragmentation - when really the issue is the ratio of resources allocated to Garbage Collection. In products which have reserved enough CPU power, internal R/W bandwidth and over-provisioning this "performance degradation" does not occur - or is minimal. For example systems from Violin Memory.

The term Garbage Collection was 1st used in 2002 - in an article we published about flash SSD reliability. Here's the definition below from that article.

The "Garbage Collection Process" eliminates the need to perform erasure of the whole block prior to every write. The "Garbage Collection process" accumulates data marked for erase as "Garbage" and perform whole block erase as space reclamation in order to reuse the block.
Can you trust your flash SSD specs & benchmarks?

GBIC GigaBit Interface Converter:- an interface module which converts the light stream from a fibre channel cable into electronic signals for use by the network interface card. Fibre channel GBIC's

Gigabyte Gigabyte abbreviated as G or GB, is a measure of the size of storage. It's equal to 1,024 Megabytes. This is about one and a half times the capacity of a standard music CD-ROM, or about a million times the capacity of a standard 3.5 inch floppy disk.

HAMR Heat Assisted Magnetic Recording technology records data magnetically on high-stability media using laser thermal assistance. HAMR, combined with self-ordered magnetic arrays of iron-platinum particles, is expected to break through the so-called superparamagnetic limit of magnetic recording by more than a factor of 100 to ultimately deliver storage densities as great as 50 terabits per square inch.

...from a featured press release by Seagate

HBA Host Bus Adapter:- an interface card which plugs into the computer's bus and connects it to the network. .Fibre-channel adapter cards

SCSI adapter cards

HSM Heirarchical Storage Management. Storage technologies have different characteristics in terms of access speed, density and cost. So it's not economic to use just one type of storage for all data needs. Luckily some data is needed more frequently than other data, so it's possible to manage the data which is stored in a heirarchy which matches the organization's applications and economics, and moves data up or down from RAM, local disk, network attached RAID, optical jukebox, tape library, web storage etc as needed. Backup software & HSM

HVD Holographic Versatile Disc. First units are expected to have 200 Gbytes capacity. Based on a technology originally developed by Optware. Storage Media

IDE Intelligent Drive Electronics is an interface standard which was developed as a low cost method of connecting a native PC bus to a mass storage device such as a disk drive. .

IEEE 1394 Also known by the names:- FireWire (Apple Computer), and i.LINK. IEEE 1394 is a high speed serial standard used for connecting external devices such as digital video cameras, and tape drives to PC's. IEEE 1394 is capable of transferring data at speeds of up to 400 Mbps, making it the perfect choice for high-speed data storage. Other FireWire benefits include its flexible connectivity and the ability to link as many as 63 devices.

...from featured press release about Ecrix
FireWire storage

ICSC Interconnect Software Consortium. Formed January 28, 2002 under the auspices of The Open Group.

"The Founding Members of the ICSC will lead the industry in developing software specifications that enable successful deployment of next-generation, fast interconnects, including the emerging InfiniBand™ specification," said Allen Brown, President and CEO of The Open Group. "The Open Group is proud to demonstrate our strong commitment to the rapid uptake of such solutions by providing infrastructure services to the ICSC."

Founding Members of the Consortium are Compaq, Fujitsu, Hewlett-Packard, IBM, Network Appliance, Sun Microsystems, and VIEO.
The Open Group


ILM Information Lifecycle Management

article:- Email Archiving and ILM - by StorageTek

InfiniBand InfiniBand is an interconnect or I/O architecture that connects servers with remote storage and networking devices, and other servers. It can also be used inside servers for inter-processor communication. InfiniBand is a channel-based, switched fabric, point-to-point interconnect, which provides scalability and performance for a wide range of platforms and price performance points.

InfiniBand provides a scalable performance range of 500 MB/s to 6 GB/s per link, meeting the needs from entry level to high-end enterprise systems.

...from featured press release about RedSwitch
InfiniBand Trade Association


iPEM Integrated Plastic Encapsulated Microcircuit - term used by military chip companies such as Austin Semiconductor - to differentiate chip products from traditional ceramic packaged devices.

iSCSI iSCSI is a software package which emulates SCSI protocols, but the connection method is via an IP network instead of a direct SCSI compatible cable.

SCSI is an intelligent protocol which enables data blocks to be read from or sent at high speed to a storage device such as a disk or tape drive. Early implementations of SCSI used ribbon cable and industry standard logic levels.

The promise of iSCSI is that storage management software which was orginally written for the well established SCSI standard, can now be used to make a remote disk or tape drive on a network operate just like a local disk. The network can be a local area network such as ethernet, or even the Internet. The potential benefit is that users can connect to remote storage devices to replicate data without having to invest in writing huge amounts of new (buggy) software.

JBOD Just a Box Of Disks:- is a term used for a storage enclosure which is supplied with disk drives pre-integrated. The systems integrator can incorporate their own choice of RAID controller or just use the JBOD as an economic way to add more disk storage. Storage Enclosures

JEDEC Joint Electronic Device Engineering Council. JEDEC is the solid state standardizing body of the Electronic Industries Alliance (EIA), the national trade organization representing manufacturers in all areas of electronics. Since 1958, JEDEC has been the leading developer of standards for the solid state industry.

...Among other things, JEDEC helps to achieve standardisation in the pinouts of memory chips. That activity means that multiple interchangeable sources are available for new product generations at launch time.

Jiro Jiro technology, originally developed by Sun Microsystems, is an open, freely available set of APIs based on the Java[tm] 2 platform that provides developers with an infrastructure for building interoperable end-to-end storage management solutions for heterogeneous environments. Jiro resources on Sun Microsystems site

LDAP Lightweight Directory Access Protocol

"Installed into a company's IT infrastructure, an LDAP server centralizes network user information. It can manage server access levels for each employee and offer an online directory including contact details such as email address, direct phone line, photo, etc. Widely used solutions like SuSE Linux OpenExchange include an LDAP server."

...from a press release by Arkeia

LPSDRAM Low-Power Synchronous Dynamic Random Access Memory RAM

LTO Linear Tape-Open (LTO) technology was developed jointly by HP, IBM and Seagate to provide a clear and viable choice in an increasingly complex array of tape storage options.

LTO technology is an "open format" technology, which means that users will have multiple sources of product and media. The "open" nature of LTO technology also provides a means of enabling compatibility between different vendors' offerings.

The Accelis format is the "fast access" implementation of LTO technology.

The Ultrium format is the "high capacity" implementation of LTO technology.

...from LTO web site

LUS A RAID not connected to anything at all can be called a LUS (Lonely Unloved Storage)...

No, I just made this one up.
RAID systems

Megabyte Megabyte abbreviated as M or MB, is a measure of the size of storage. It's equal to

1,024 x 1,024 = 1,048,576 bytes.

In the early days of computing this was considered to be quite a large amount of data. Nowadays when many new PC's comes with over 256M RAM the unit of a Megabyte seems quite small to most users.
Megabyte is also the name of our editor. See more about Megabyte the Mouse.

MEMS Micro-Electro-Mechanical Systems are microscopic devices that are produced on semiconductor chips and are measured in micrometers.

...from a press release by Nanochip

MLC MLC (Multi Level Cell) is a term used in the context of flash memory to describe how the storage charge in a single floating gate transistor cell is interpreted by the logic system.

In traditional digital systems, the change in state (of a voltage, current or charge) is interpreted as being either 1 of 2 distinct levels - "0" or "1" - which is where we get the term binary logic from. Such flash cells are called SLC (Single Level Cell).

In an MLC memory chip the stored charge is interpreted as a range of values (0 to 3), (0 to 7) etc - which depends on the ability of the discrimator circuits surrounding the memory array to reliably tell the difference between levels.

The logical memory capacity of a such a cell is 2 bits, or 3 bits etc - where the bits are binary.

Discriminating multiple levels is difficult to achieve technically - because it involves an analog to digital conversion process - and due to manufacturing tolerances the same charge may not represent the identical value in another part of the chip.

There are also various factors which make the process unrepeatable - by dumping charge into the cell when adjacent parts of the chip are being written to, by leakage from the cell into the substrate over time, and by damage in the transistor material due to successive writes (endurance).

MLC designers overcome these problems (which become harder in each shrink generation) by wrapping blocks of memory in protective error correction and detection codes.

Because the charge in an MLC cell is interpreted as 2x, 4x etc more data than in the same geometry level SLC chip - MLC is much more sensitive to age and wear-out factors than SLC. That's why oems typically quote an endurance figure which is 10x lower.
MLC - editor mentions on

Are MLC SSDs Ever Safe in Enterprise Apps?

MMC MultiMediaCard - a format for flash memory. Flash Memory

MRAM Magnetic Random Access Memory - MRAM combines the best features of today's common memory technologies: the storage capacity and low-cost of DRAM, the high speed of SRAM, and the non-volatility of flash memory. Expected to appear in products in 2005.

...from a featured release by Infineon Technologies
RAM manufacturers

NANO CUBIC technology NANO CUBIC technology is an ultra-thin layer coating that results in higher resolution for recording digital data, ultra-low noise and high signal-to-noise ratios that are ideal for magneto-resistive (MR) heads. It is capable of catapulting data cartridge and digital videotape to one-terabyte native (uncompressed) capacities and floppy disk capacities to three gigabytes. To help visualize the potential, 1TB can store up to 200 two-hour movies. What sets the NANO CUBIC coating technology apart is its ability to be applied cost-effectively to a mass production manufacturing process while requiring only small modifications to current coating equipment for application. Fujifilm is beginning to work with drive manufacturers to develop new, high capacity magnetic storage products using NANO CUBIC technology.

...from a featured release by Fujifilm

NAS Network Attached Storage - is a term used for RAID, tape and other mass storage systems which have an integral network connection such as ethernet or fibre-channel, These devices can be connected as a network resource rather than just attached to a particular server. A Storage Architecture Guide - white paper by Auspex Systems

Network Attached Storage

Nibble Nibble is a unit of information equal to 4 bits (or half a byte). This was a useful term back in the 1970's if you were hand coding microprocessor assembler in the days when an Intel development system cost more than the average engineer's house. .

NIC Network Interface Card. This term is mainly used in the context of switch manufacturers. However the same card when plugged into a server may be called an HBA. Fibre channel switches & hubs, Ethernet Switches

NUS Network Unified Storage is a RAID system connected by both Fibre-channel and Ethernet. RAID systems

Fibre-channel adapter cards

Over-Provisioning Over-Provisioning is a technique used in the design of some flash SSDs. By providing extra memory capacity (which the user can't access) the SSD controller can more easily create pre-erased blocks - ready to be used in the virtual pool. 2 beneficial effects of Over-Provisioning are:- faster overall write IOPS, and better reliability. The latter case - is because another use of the extra capacity is to replace bad memory blocks - which occur at both ends of the bathtub curve.

PACS Picture Archiving and Communication Systems (medical context) .

Petabyte A Petabyte is 1,024 Terabytes, or just over a million gigabytes. How much data is that? A press release from StorageTek in March 2003 said that their customer National Center for Atmospheric Research had just surpassed the one-petabyte mark in its data holdings, which range from satellite, atmosphere, ocean, and land-use data to depictions of weather and climate from prehistoric times.

To help visualize this quantity, StorageTek said that a petabyte of data is the equivalent of 500 billion pages of standard printed text. That's enough data to fill 500 million floppy disks and enough information to fill the Library of Congress 100 times.

pNFS Parallel Network File System - initially created and developed by Panasas. NAS

PRAM Phase-change Random Access Memory.A new non-volatile RAM technology. First working prototypes announced by Samsung Electronics in September 2006. Samsung said PRAM is expected to replace high density NOR flash within the next decade

PRML Partial Response, Maximum Likelihood - technology is used in the read channel of DVD media controller chips.

PSRAM Pseudo Static RAM. This new type of Pseudo SRAM device is designed to meet the rapidly growing memory and bandwidth demand in 2.5G and 3G handset designs, at a lower cost/bit ratio than current or proposed alternatives. Featuring SRAM-pin compatibility, refresh-free operation and extreme low power design, CellularRAM memory is a drop-in replacement for the asynchronous low power SRAM typically used in today's cell phone designs. CellularRAM is based on a single transistor DRAM cell versus a six-transistor (6T) SRAM cell.

...from a featured press release by Infineon Technologies
RAM manufacturers

QBM Quad Band Memory is a memory bus technology used to connect RAM on motherboards. It's being positioned as an industry standard to succeed DDR.

...from a featured Kentron Technologies press release November 15, 2001
QBM Alliance

RAID Redundant Array of Inexpensive Disks. In the 1980's when this term was originated, by IBM, you could buy 2 types of disk drives, either low cost drives such as used in the average PC, or high speed high performance drives as used in digital video effects systems or mainframes. Because of the larger market for PC disks, they eventually became the technology drivers and effectively killed off the higher cost alternatives. However the original concept remains valid. You can create a disk array which looks electronically just like a bigger ordinary disk, by attaching a bunch of disks working in parallel and connected to a RAID controller interface.

The combined system can be programmed to provide desirable characteristics such as faster data throughput (for example a 4 disk wide system could have a data throughput capability 4 times faster than a single disk). RAID can also provide fault tolerance, because redundant disks can be added into the array and the data split up in such a way that there is no loss of performance or data ability if any single disk fails. However, RAID doesn't speed up access time, which is why some applications also use solid state disks.
RAID controller cards, RAID systems

RAIGE RAID Across Independent Gigabit Ethernet) is a creation of Pivot3 although some of concepts sound similar to how Google implements its internal storage infrastructure.

RAIN Redundant Array of Independent Nodes is an Adaptec creation

RDMA Remote Direct Memory Access (over over TCP/IP, Ethernet and other networks). RDMA technology enables high-performance server clustering and eliminates the burden of excessive memory copies when communicating between servers.

...from a press elease by Neterion

Regular flash SSD Classification defined in the article RAM Cache Ratios in flash SSDs. A self referential definition - "Regular flash SSD" is the design choice used in most flash SSDs currently in the market

RLDRAM Reduced Latency DRAM. Designed specifically for use in high-speed networking and fast cache applications, RLDRAM is an ultra-high speed Double Data Rate (DDR) SDRAM that combines fast, random access with extremely high bandwidth and high density.

...from a featured press release by Infineon Technologies

ROC RAID on Chip storage chips

ROMB RAID on motherboard RAID controllers

RRAM Resistive RAM is a technology being researched (in 2008) by IMEC. It could be at least another 5 years before any commercial products result from this (if ever). nv memory

SAID Self-maintaining Array of Identical Disks - from Atrato

S-AIT S-AIT is a new data storage technology platform based on Sony's Advanced Intelligent Tape recording format and areal densities. S-AIT is based on high-density helical-scan technology utilizing Advanced Metal Evaporated (AME) media in a single-reel, half-inch cartridge design. The first generation product is expected to yield one-half terabyte of capacity in a single-reel, half-inch tape cartridge, with an expected roadmap capability up to four terabytes.

Unlike traditional tape technology where less than 50 percent of the recording layer is comprised of magnetic material, the 'evaporated' metal recording layer of AME tape is almost 100 percent magnetic material, enabling greater recording density and storage capacity per cartridge. This also provides a smoother tape surface, providing significantly longer head life and eliminating the need for periodic cleaning.

...from a featured press release, November 2, 2001 - from Sony announcing the new technology

SAM Storage Area Management

...from a July 2002 document by EMC and Gartner

SAN Storage Area Network. This term was first coined to describe networks based around fibre-channel, but nowadays SAN's can also be include other connection technologies such as ethernet and even the internet. SAN is really a networking concept in which the software has a knowledge of the quantity and value of data stored in mass storage devices and the characteristics of those storage devices. In a way SAN is a superset of traditional networking thinking. In SAN systems it's not just enough to know that data is moving from A to B. The software also has to know about the backup strategy, data recovery and application software specific attributes to preserve and reconstruct the environment in case of a failure or system reconfiguration. This aims to automatically replicate many functions which were previously managed by people called systems administrators. article:- SAN Applications - by Farid J. Neema - President of Peripheral Concepts, Inc

Squeak! - Breaking the SAN Babble - the mouse speaks

SAN - all, SAN - software, SAN training companies

SANmark The SANmark Qualified Program is sponsored, operated, and promoted as an open industry, conformance test suite development program, within the non-profit Fibre Channel Industry Association (FCIA). This program addresses product interoperability and device level compatibility for companies participating in the program. The program is open to members and non-members of the FCIA organization, and is intended to benefit the entire storage networking industry at large. To get involved in the program or ask questions, please send an email to

...from a featured press release - November 6, 2001 - by Gadzoox Networks

SBOD Switched Bunch Of Disks

...from a featured press release - September 8, 2003 - by Vixel
Fibre channel switches

SBus SBus is a host bus interface introduced by Sun Microsystems in the SPARCstation 1 desktop workstation in 1989. In the years which followed, the standard was used by over 250 manufacturers which made products for Sun and Sun compatible systems. It was superceded when Sun adopted the (later developed and similar) PCI bus 1996. However because of the large installed base, oem's were still anouncing SBus cards in 2000. article:- SBus, SCSI, PCI, compactPCI and other busses used in SPARC based systems

SBus Product Directory (& PCI cards)

SCSI Small Computer System Interface:- is a high performance parallel interface for connected mass storage devices such as disk drives to a computer. Originally specificied using logic level (TTL) signals over ribbon cable to daisy chain upto 8 devices, this standard has been enhanced over the years to include newer voltage levels, higher speeds and more devices. The standard enables large amounts of data to be requested using a small number of intelligent commands. Dur to the popularity of this standard some manufacturers have developed extenders which enable connection over a long distance, converters such as IDE to SCSI, and routers which translate the SCSI interface and commands to fibre channel compatible signals. article:- LVD, SE, HVD, SCSI compatibility - or lack of it - by Paralan,

article:- What is SCSI? - an overview - by Performance Technologies

SCSI Trade Association

SCSI Glossary - by Paralan

SCRAMNet Shared Common RAM Network, is Curtiss-Wright Controls' multi-platform, replicated shared memory architecture. A SCRAMNet network uses a ring topology that supports up to 256 nodes. The resulting multi-processor system provides host-processor and operating system independence at each node. It's designed for use with real-time fiber optic communication systems and is optimized for the high-speed transfer of small data packets between computers when ultra-low latency data transmission is required. SCRAMNet's inherent low-latency performance supports the tight control-feedback loops required by many instrumentation and control systems.

Serial ATA Serial ATA is a storage interface specification for the next-generation computing platform. This interface is used to connect storage devices, such as hard disc drives, DVDs and CD-R/Ws, to the motherboard and is the replacement for today's Parallel ATA physical storage interface.

Serial ATA technology will allow for platform cost reductions and performance improvements while supporting a seamless transition from Parallel ATA technology. Serial ATA will supply storage interface headroom for many generations to come, beginning with 1.5 Gbps, and scalable to 2x, 4x and beyond. At the same time, Serial ATA is a drop-in solution that is compatible with existing ATA software drivers and will run on standard operating systems without modification. It will provide for systems that are easier to design, with narrower cables that are simple to route and install, smaller cable connectors, improved silicon design, and lower voltages, which alleviate current design constraints in Parallel ATA. Configuration of Serial ATA devices will be much simpler, with many of today's requirements for jumpers and settings no longer needed.

...from a featured Seagate Technology press release Feb 2001
Serial ATA

Serial ATA Working Group

Serial Attached SCSI First announced in November 2001, the first functioning silicon for this was demonstrated in January 2004 by LSI Logic. Host Bus Adapters and chipsets supporting this new standard start shipping to storage system designers in April/May 2004 from various companies. But we're not expecting to see any real products which users can get their hands on until much later - towards the end of 2004. Serial Attached SCSI

SiSMART SiSMART monitors how many write/erase cycles have occurred on a solid-state flash storage system -- the only real failure mechanism present in solid-state storage. By incorporating a patent-pending algorithm that tracks all data transactions internally in the SiliconDrive, SiSMART is able to accurately monitor and report storage system usage to the host system. This enables users to model future usage, set thresholds to perform maintenance and adjust data collection requirements to match the required life of the deployed equipment.

...from a press release by SiliconSystems

Skinny flash SSD Classification defined in the article RAM Cache Ratios in flash SSDs. These are designs which include miniscule amounts of RAM - orders of magnitude smaller than Regular flash SSDs.

SMART Technology Rotating hard disk drives employ Self Monitoring and Reporting Technology (SMART), which was designed to act as an early warning system for pending problems with mechanical media.

...from a press release by SiliconSystems

SSF Formed under the auspices of the Storage Networking Industry Association (SNIA) and the Technical Support Alliance Network (TSANet), the SNIA Supported Solutions Forum (SSF) provides a process for coordinating rapid response technical support for multi-vendor storage networks that use interoperable products from member companies. The organization certifies multi-vendor solutions as interoperable, and it provides a mechanism for technical support professionals from all of the participating companies to take rapid, coordinated action to support joint customers. The program includes 7x24 support and extends to sites around the world. Supported Solutions Forum

SFP Small Form-factor Pluggable (GBIC) provides the same functionality as a regular GBIC but in a smaller and denser physical size. It's used in network switches for Fibre-channel, Gigabit Ethernet and Infinband. The newer generation of SFPs operates at faster data transfer rates of 2.5 Gbps and above.

...from a featured press release January 2002
GBICs and SFPs

SGNP Secure Grid Naming Protocol is an elegant solution that delivers a scalable, global name space, a built-in method for associating security information with such names, and migration transparency. The global name space, scalable to literally trillions of named resources or services, is designed to unify multiple or conflicting naming schemes, allowing any resource or service to be found and communicated with using the same name across an entire grid. SGNP's security model eliminates the need for a central trusted authority, which is a major barrier to grids extending beyond a single enterprise today. Finally, the enabling of migration transparency gives grid solution providers the ability to move processes or data without impacting work in progress or needing to inform end users. It allows grid resources to continue reliably communicating with one another in the face of any number of challenges.

...from a featured press release by Avaki February 2002

SLR SLR is a trademark of Tandberg Data. It relates to a family of compatible tape drives and media. SLR tape drives offer capacities from 525 MB to 100GB and up to 4TB with SLR automation In March, 2001 - Tandberg Data announced that it had shipped its third million SLR tape drive to the market. Tape drives & systems

SMI-S Storage Management Initiative Specifications

SNIA Storage Networking Industry Association Industry trade associations

SODIMM Small Outline Dual In-line Memory Module

...from a featured Kentron Technologies press release March 14, 2001

Solid State Disk A Solid State Disk (SSD) is a semiconductor system which functions just like a disk drive, but which contains no moving parts. The advantages are faster access time and better resilience to vibration and temperature. The disadvantages are higher cost (more expensive per megabyte than disk drives) and larger size (an individual SSD can be mechanically compatible with a winchester disk drive, but because it has lower capacity, more drives will be needed to implement the same storage capacity.) Solid State Disks - introduction, applications & FAQ's - white paper by Curtis, Inc.

SONOS Silicon-Oxide-Nitride-Oxide-Silicon is a non volatile memory technology. Silicon Nitride NV memories first came to market in the late 1970s but suffered from low data retention life compared to EPROM and disappeared from view. More recently, in 2006, SONOS is making a comeback in some applications because of better scalability with small chip geometries than flash.

SOX Sarbanes-Oxley - usually referred to in the context of compliance. article:- Privacy and Security Regulations, and How they Impact Storage Systems

SPARC Scalable Processor ARChitecture:- a processor architecture created by Sun Microsystems, which first appeared in commercial systems in 1987. SPARC history article:- History of SPARC systems

the SPARC Product Directory

SPC The Storage Performance Council is the only industry standards organisation that defines and promotes storage benchmarks as well as disseminates objective, relevant and verifiable performance data and related test tools to the computer industry and its customers. Storage Performance Council

SRM Storage Resource Management software keeps track of the utilization of storage devices in a network and warn system administrators before they run out of disk space. Software

SSP Storage Service Provider. Although most recent examples are companies which sell storage via the web, other examples include content delivery with agreed service levels, storage security monitoring, web backup, on-site storage management etc. Services (SSP's) , Web based storage

Super DLTtape Quantum Corporation's new Super DLTtape technology provides 110 GB (native) capacity per cartridge and 39.6 GB/hour (native) throughput per drive, nearly tripling the data storage capacity and doubling the throughput of previous generation DLTtape technology. Super DLTtape technology integrates seamlessly into existing systems, offering backward-read compatibility with multiple generations of DLTtape drives and millions of DLTtape IV data cartridges.

...from a featured ADIC press release July 18, 2001
Tape drives & systems

Terabyte Terabyte abbreviated as T or TB, is a measure of the size of storage. It's equal to 1,024 Gigabytes. That's about 50 times the size of a typical PC disk drive. This unit of storage is most commonly used for backup devices such as tape drives and tape libraries. We thought that Terrabyte was a pretty scary measure of storage size, so we used it in naming the character associated with tape libraries on this site:- Terrorbyte.

TeraGlob TeraGlob is a word invented by's editor. Here's the original citation below.

HP Announces TeraGlobs of New Storage

LAS VEGAS - May 16, 2005 - In the most significant expansion of its storage portfolio in company history, HP today unveiled numerous new products and services.

Announced at the HP Americas StorageWorks Conference, the new and enhanced offerings are the result of investments, innovations and alliances across an HP StorageWorks portfolio designed to help customers put their information to work. The deep integration across HP's entire storage portfolio results in streamlined customer IT environments by leveraging HP's leadership in servers, management software and services - bringing businesses one step closer to becoming Adaptive Enterprises able to synchronize business and IT to capitalize on change. ...HP profile

Editor's comments:- It's a shame but, as is often the case with HP's storage news releases, the sheer quantity of new products announced in one day buries anything good under a pile of mediocrity. As users know "quantity" is not the same as "quality" and maybe that's one reason why HP's storage business has been failing to make the benchmark business growth set by its peers and rivals. HP marketers would probably do better to let their storage product managers do individual launches instead of these big corporate TeraGlobs. What's a TeraGlob? I made the word up and there are zero instances on over 8 billion pages of Google. But it sounds like a word that's needed in cases like this.

TOE TCP/IP offload engine is a hardware accelerator which offloads iSCSI and related processing from the host processor iSCSI and FCIP

TSANet Founded in 1993, TSANet (Technical Support Alliance Network) is a worldwide, multivendor alliance that offers an industry-wide forum to facilitate servicing multivendor customers while providing an infrastructure for more efficient multivendor problem solving. Membership consists of more than one hundred software and hardware companies, including industry giants such as EMC, HP, IBM, Microsoft, Novell, Sun Microsystems, Unisys, and Veritas. TSANet

UDO Ultra Density Optical, the next generation 5.25-inch optical drive technology. UDO will utilize 405nm blue-violet laser and phase change technology from the recently announced consumer DVD type products. UDO media cartridges will be dimensionally identical to current 5.25-inch MO to provide compatibility with existing 5.25-inch library automation and both WORM and rewritable media will be available. The first generation product will provide 30GB capacity and a fast data transfer rate of up to 8MB/s. Future generations will increase capacity to 60GB and 120GB and backward read capability will be maintained throughout the product roadmap.

...from a featured press release by Plasmon

Ultra320 A variant of the SCSI standard which supports data transfer speeds upto 320 Megabytes per second. SCSI Trade Association

Unified Storage "Unified storage has been defined as a single integrated storage infrastructure that functions as a unification engine to simultaneously support Fibre Channel, IP SAN and NAS data formats." - from a press release by ONStor

USB The USB (for Universal Serial Bus) is a low cost serial bus which can provide upto 12 Mb/S. That's about 100 times faster than the RS-232 style serial interfaces used in earlier generations of computers.

First developed in 1996, the USB is now widely used in Macs, PC's and even Linux systems. USB is typically used to connect devices such as printers, scanners, keyboards, digital cameras, MP3 players and low speed storage devices.

In June 2002, Intel and others started to demonstrate USB 2.0, which increases the speed of the peripheral to PC connection from 12 megabits per second (Mbps) on USB 1.1 to up to 480 Mbps on USB 2.0, or 40 times faster than with the older technology.
USB - drives

USB trade organization

VI Architecture Virtual Interface Architecture. In December 1996, several companies established the VI Architecture consortium to study methods for lowering the excessive overhead of traditional I/O software for data center networks. More than 100 hardware and software vendors defined the version 1.0 VI Architecture standard.

The VI Architecture defines how an agent initiates the connection between two nodes, much like other types of network connections. After initiation, a direct connection between user agent memory (or virtual interface protocol layer) and the hardware allows a direct memory copy between two nodes using the VI communication channel. These communications can be performed directly by memory-mapped I/O or by using additional layers to adapt from the VI structure to internal data formats.

...from a featured press release by QLogic

VXA VXA is the trademarked name for a tape technology developed by Ecrix.(which merged with Exabyte)

VXA incorporates three major innovations in tape storage: Discrete Packet Format (DPF)™ , Variable Speed Operation (VSO)™ , and OverScan Operation (OSO)™ .
  • DPF enables data to be written and read in individually addressed packets, a technology similar to that already proven in the networking and Internet markets.
  • VSO saves time by continually adjusting tape speed to match the varying data throughput of the server, eliminating a common streaming tape problem known as "backhitching."
  • OSO is a technique for reading data packets independent of track shape or geometry. By overscanning data packets at variable tape speeds, VXA virtually guarantees data restore.
These three innovative features enable VXA drives to offer previously unattainable levels of reliability, recoverability, capacity and interchangeability. VXA technology also permits drive and alignment mechanisms to be much simpler and less sensitive to environmental factors, resulting in enhanced manufacturability and significantly lower cost.

...from Ecrix Fact Sheet

Wear Leveling Wear Leveling is a technique used inside flash SSDs to prolong the life of a flash memory array.

Countering the phenomenom called endurance - Wear Leveling processes in the SSD controller keep track of how many erase cycles have been performed on each flash block - and dynamically remap logical to physical blocks using algorithms which spread out the wear over the whole population in the array. Working hand in hand with over-provisioning - bad cells (which wear-out earlier than the median life) can be replaced - considerable extending SSD life.

There are 3 levels of wear leveling used in the best server grade SSDs - static, dynamic and active.
Rugged & Reliable Data Storage: Solid-State Flash Disks overview

Increasing Flash Solid State Disk Reliability

SSD Myths and Legends - "write endurance"

Are MLC SSDs Ever Safe in Enterprise Apps?

WORM Write Once Read Many times. Many types of storage media are available which offer this mode of operation preventing accidental or deliberate over writes of critical data.

XFP XFP = 10-Gigabit Small Form-factor Pluggable GBIC Module for the telecommunications, data communications and SAN markets. These transceivers are designed to occupy one-fifth of the space and dissipate one-half the power of current 10Gb/s modules.

...from a featured press release by Finisar

GBICs and SFPs

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