glossary | DataRecoveryUnion.com

SaaS: Software as a Service
Software as a Service (SaaS) is a software delivery method that provides access to software and its functions remotely as a web-based service. Software as a Service allows organizations to access business functionality at a cost typically less than paying for licensed applications since SaaS pricing is based on a monthly fee. Also, because the software is hosted remotely, users don’t need to invest in additional hardware. Software as a Service removes the need for organizations to handle the installation, setup, and often daily upkeep and maintenance. Software as a Service may also be referred to as simply hosted applications.

SaaS: Storage as a Service
Storage as a Service (SaaS) is a storage model in which a business or organization (the client) rents or leases storage space from a third-party provider. Data is transferred from the client to the service provider via the Internet and the client then accesses the stored data using software provided by the storage provider. The software is used to perform common tasks related to storage, such as data backups and data transfers. Storage as a Service is popular with SMBs because there usually are no start-up costs (for example, servers, hard disks, IT staff, and so on) involved. Businesses pay for the service based only on the amount of storage space used. Storage as a Service may also be called hosted storage.

SAN
A Storage Area Network (SAN) is a high-speed subnetwork of shared storage devices. A storage device is a machine that contains nothing but a disk or disks for storing data. A SAN’s architecture works in a way that makes all storage devices available to all servers on a LAN or WAN. As more storage devices are added to a SAN, they too will be accessible from any server in the larger network. In this case, the server merely acts as a pathway between the end user and the stored data. Because stored data does not reside directly on any of a network’s servers, server power is utilized for business applications, and network capacity is released to the end user.

SAN fabric
The hardware that connects workstations and servers to storage devices in a SAN. The SAN fabric enables any-server-to-any-storage device connectivity through the use of Fibre Channel switching technology.

SAN services
A technology used by businesses to obtain greater flexibility in their data storage. A Storage Area Network (SAN) provides raw storage devices across a network, and is typically sold as a service to customers who also purchase other services. SAN services may also be administered over an existing, local fiber network, and administered through a service subscription plan.

Scratch disk
Space dedicated on a hard drive for temporary storage of data. Scratch disks are commonly used in graphic design programs, such as Adobe Photoshop. Scratch disk space is only for temporary storage and cannot be used for permanently backing up files. Scratch disks can be set to erase all data at regular intervals so that the disk space is left free for future use. The management of scratch disk space is typically dynamic, occurring when needed.

Seed
The first full backup of company data.

Secret storage technology
A technology for encrypting and hiding data on a hard drive, flash drive, or when transferring files. Secret storage is a portion of encrypted data, hidden in some file or FAT/FAT32/NTFS partitions. To the end-user, it looks like a folder in which he may add files and folders and protect it with a password.

Selective backup
A type of backup where only the user-specified files and directories are backed up. A selective backup is commonly used for backing up files which change frequently or in situations where the space available to store backups is limited. Also called a partial backup.

Serial storage architecture
Serial storage architecture (SSA) is an open industry-standard interface that provides a high-performance, serial interconnect technology used to connect disk devices and host adapters. SSA serializes the SCSI data set and uses loop architecture that requires only two wires: transmit and receive. The SSA interface also supports full-duplex, so it can transmit and receive data simultaneously at full speed.

Server cage area
The area where a company stores its data center equipment. This area is protected from personnel access.

Service-level agreement
A service-level agreement (SLA) is an agreement between a service provider, such as an IT department, an Internet services provider, or an intelligent device acting as a server, and a service consumer. A service level agreement defines parameters for measuring the service, and states quantitative values for those parameters.

Slack space
The unused space in a disk cluster. The DOS and Windows file systems use fixed-size clusters. Even if the actual data being stored requires less storage than the cluster size, an entire cluster is reserved for the file. The unused space is called the slack space. DOS and older Windows systems use a 16-bit file allocation table (FAT), which results in very large cluster sizes for large partitions. For example, if the partition size is 2 GB, each cluster will be 32 K. Even if a file requires only 4 K, the entire 32 K will be allocated, resulting in 28 K of slack space. Windows 95 OSR 2 and Windows 98 resolve this problem by using a 32-bit FAT (FAT32) that supports cluster sizes smaller than 1K.

Small and medium enterprise (SME)
Companies whose headcount or turnover fall below certain limits. In the United states, a small business is often defined as having fewer than 100 employees. A medium-size business is often defined as having fewer than 500 employees.

Small to mid-size business (SMB)
Companies whose headcount or turnover fall below certain limits. In the United states, a small business is often defined as having fewer than 100 employees. A mid-size business is often defined as having fewer than 500 employees.

Snapshot backup
A virtual copy of a device or file system. Snapshots imitate the way a file or device looked at the precise time the snapshot was taken. It is not a copy of the data, only a picture in time of how the data was organized. Snapshots can be taken according to a scheduled time and provide a consistent view of a file system or device for a backup and recovery program to work from.

Solid state disk
A solid state disk (SSD) is a high-performance plug-and-play storage device that contains no moving parts. SSD components include either DRAM or EEPROM memory boards, a memory bus board, a CPU, and a battery card. Because SSDs contain their own CPUs to manage data storage, they are a lot faster (18MBps for SCSI-II and 35 MBps for UltraWide SCSI interfaces) than conventional rotating hard disks; therefore, they produce highest possible I/O rates.

Spin valve
Another name for a giant magnetoresistive(GMR) head. The term was coined by IBM.

Storage

The capacity of a device to hold and retain data.
Short for mass storage.

Storage bay bridge
Storage bridge bay (SBB) is a specification that defines mechanical, electrical, and low-level enclosure management requirements for an enclosure controller slot that will support a variety of storage controllers from a variety of independent hardware vendors and system vendors. Any storage controller design based on the SBB specification will be able to fit, connect, and operate within any storage enclosure controller slot design based on the same specification.

Storage Consolidation
The concept of centralized storage where resources are shared among multiple applications and users. Traditionally, organizations have deployed servers with direct-attached storage (DAS) as file servers. However, many organizations are facilitating server consolidation by deploying network-attached storage (NAS). NAS provides a single purpose device that can provide CIFS and NF- connected storage that can scale from gigabyte to petabytes.

Storage device
A device capable of storing data. The term usually refers to mass storage devices, such as disk and tape drives.

Storage footprint
The amount of energy, physical space, and other equipment necessary to run a data storage management system.

Storage management
The tools, processes, and policies used to manage storage networks and storage services such as virtualization, replication, mirroring, security, compression, traffic analysis, and other services. The phrase also encompasses other storage technologies, such as process automation, storage management and real-time infrastructure products, and storage provisioning. In some cases, the phrase storage management may be used in direct reference to storage resource management (SRM).

Storage management initiative specification
Storage management initiative specification (SMI-S) is an interface standard that enables interoperability in both hardware and software between storage products from different vendors used in a SAN environment. The interface provides common protocols and data models that storage product vendors can use to ensure end user manageability of the SAN environment.

Based on the CIM and Web-Based Enterprise Management (WBEM) standards, SMI-S adds common interoperable and extensible management transport, automated discovery, and resource locking functions. SMI-S was developed by the Storage Networking Industry Association (SNIA) in 2002.

Storage networking
A high-speed network of shared storage devices. The storage network is used by IT departments to connect different types of storage devices with data servers for a larger network of users. As more storage devices are added to the storage network, they too will be accessible from any server in the larger network. Storage networking is a phrase most commonly associated with enterprises and data centers.

Storage optimization
The implementation and management of tiered storage solutions to obtain a lower cost per capacity across a corporation or enterprise. Storage optimization is an information lifecycle management (ILM) strategy.

Storage over IP
Storage over IP (SoIP) technology refers to the merging of Fibre Channel technologies with IP-based technology to allow for accessing storage devices over TCP/IP networks. SoIP is the framework for storage area networking (SAN) using Internet Protocol (IP) networks to directly connect servers and storage. SoIP products are designed to support transparent interoperability of storage devices based on Fibre Channel, SCSI, and a new class of Gigabit Ethernet storage devices using iSCSI and iFCP. Existing Fibre Channel or SCSI devices, such as servers with host bus adapters (HBAs) or storage subsystems, can be included in an SoIP storage network without modification.

Storage resource management
Storage resource management (SRM) refers to software that manages storage from a capacity, utilization, policy, and event management perspective. SRM includes bill-back, monitoring, reporting, and analytic capabilities that allow you to drill down for performance and availability.
Key elements of SRM include asset management, charge back, capacity management, configuration management, data and media migration, event management, performance and availability management, policy management, quota management, and media management.

Storage service provider
A storage service provider (SSP) is a company that provides computer storage space and related management services. SSPs also offer periodic backup, archiving, and the ability to consolidate data from multiple company locations so that data can be effectively shared.

Storage virtualization
Storage virtualization is the amalgamation of multiple network storage devices into what appears to be a single storage unit. Storage virtualization is often used in a SAN (storage area network), a high-speed subnetwork of shared storage devices, and makes tasks such as archiving, backup, and recovery easier and faster. Storage virtualization is usually implemented via software applications.

Store
To copy data from a CPU to memory, or from memory to a mass storage device.

Stripe
The process of distributing data across several storage devices to improve performance.

Superparamagnetism
In magnetic disk drive storage technology, the fluctuation of magnetization due to thermal agitation. When the areal density—the number of bits that can be stored on a square inch of disk media—of a disk medium reaches 150 gigabits per square inch, the magnetic energy holding the bits in place on the medium becomes equal to the ambient thermal energy within the disk drive itself. When this happens, the bits are no longer held in a reliable state and can “flip,” scrambling the data that was previously recorded. Because of superparamagnetism, hard drive technologies are expected to stop growing once they reach a density of 150 gigabits per square inch.

Synchronization
In Fibre Channel, a receiver’s identification of a transmission word boundary.

Synthetic backup
A synthetic backup is identical to a regular full backup in terms of data, but it is created when data is collected from a previous, older full backup and assembled with subsequent incremental backups. The incremental backup will consist only of changed information. A synthetic backup is used when time or system requirements do not allow for a full complete backup. The end result of combining a recent full backup archive with incremental backup data is two kinds of files which are merged by a backup application to create the synthetic backup. Benefits to using a synthetic backup include a smaller amount of time needed to perform a backup, and lower system restore times and costs. This backup procedure is called “synthetic” because it is not a backup created from original data.

Data Storage

Data Backup Glossary (Letter Q)

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RAID
See redundant array of independent (or inexpensive) disks.

RAIN
See redundant array of independent nodes.

Raised floor
A type of flooring supported by a metal grid and typically used in data centers. Raised flooring can be removed in pieces to allow for cabling, wiring, and cooling systems to run under the floor space. When the floor is raised, it usually can accommodate space for walking or crawling in.

Recovery
The recreation of a past operational state of an entire application or computing environment. Recovery is required after an application or computing environment has been destroyed or otherwise rendered unusable. It may include restoration of application data, if that data has been destroyed as well.

Recovery point objective
Recovery point objective (RPO) is the maximum acceptable time period prior to a failure or disaster during which changes to data may be lost as a consequence of recovery. Data changes preceding the failure or disaster by at least this time period are preserved by recovery. Zero is a valid value and is equivalent to a “zero data loss” requirement.

Recovery time objective
Recovery time objective (RTO) is the period of time after an outage in which the systems and data must be restored to the predetermined recovery point.

Red Hat Global File System
Red Hat Global File System (GFS) is an open source cluster file system and volume manager that executes on Red Hat Enterprise Linux servers attached to a storage area network (SAN). It enables a cluster of Linux servers to share data in a common pool of storage to provide a consistent file system image across server nodes. Red Hat Global File System works on all major server and storage platforms supported by Red Hat.

Redundancy
The inclusion of extra components of a given type in a system (beyond those required by the system to carry out its function) for the purpose of enabling continued operation in the event of a component failure.

Redundant array of independent (or inexpensive) disks
Redundant array of independent (or inexpensive) disks (RAID) is a category of disk drives that employ two or more drives in combination for fault tolerance and performance. RAID disk drives are used frequently on servers but aren’t generally necessary for personal computers. RAID allows you to store the same data redundantly (in multiple places) in a balanced way to improve overall performance.

Redundant array of independent nodes
Redundant array of independent nodes (RAIN) is a data storage and protection system architecture. It uses an open architecture that combines standard computing and networking hardware with management software to create a system that is more distributed and scalable. RAIN is based on the idea of linking RAID nodes together into a larger storage mechanism. In a RAIN setup, there are multiple servers, each with disk drive and RAID functionality, all working together as a RAIN, or a parity or mirrored implementation. RAIN may also be called storage grid.

Remote offices/branch offices (ROBOs)
Refers to corporate offices externally connected to a WAN or a LAN. These offices will often have one or more servers to provide branch users with file, print, and the other services required to maintain the daily routine.

Replicate
(n.) A copy of a collection of data.
(v.) The action of making a replicate as defined above.

Restore
To bring a desired data set back from the backup media.

Rotational latency
Also called rotational delay, the amount of time it takes for the desired sector of a disk (for example, the sector from which data is to be read or written) to rotate under the read-write heads of the disk drive. The average rotational latency for a disk is half the amount of time it takes for the disk to make one revolution. The term typically is applied to rotating storage devices, such as hard disk drives and floppy drives (and even older magnetic drum systems), but not to tape drives.

RPO
See recovery point objective.

RTO
See recovery time objective.

Run length limited
Run length limited (RLL) is an encoding scheme used to store data on newer PC hard disks. RLL produces fast data access times and increases a disk’s storage capacity over the older encoding scheme called MFM (modified frequency modulation).

Data Storage

Data Backup Glossary (Letter P)

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Physical erase unit
A physical erase unit is the smallest memory area of the flash memory media that can be erased in a single erase operation. Its size varies between flash devices.

Platform
A physical entity that contains nodes. Platforms include all end devices that are attached to a Fabric, for example, hosts and storage subsystems. Platforms communicate with other platforms in the storage area network using the facilities of a Fabric or other topology

Portable image storage device
A small, portable storage device used for storing and viewing your digital images. The device is a portable hard drive in an enclosure that resembles handheld game consoles. The device usually offers USB and memory card readers as options for transferring your images directly to the device, as well as an LCD display for viewing the stored images. The device may also have different controls for maneuvering through the images, such as forward, random, skip, and so on.

Primary storage
A somewhat dated term for main memory. Mass storage devices, such as disk drives and tapes, are sometimes called secondary storage.

Protocol
A set of rules that control an interaction between two or more entities in communication with one another, for example, TCP ports, Fibre Channel FC-4 processes, and polite humans.

Data Storage

Data Backup Glossary (Letter O)

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Object-based storage device
An object-based storage device (OSD) is a device that implements the standard in which data is organized and accessed as objects, where object means an ordered set of bytes (within the OSD) that is associated with a unique identifier. Objects are allocated and placed on the media by the OSD logical unit. With an OSD interface, metadata is associated directly with each data object and can be carried between layers and across storage device files. Records are no longer abstractions, but actual storage objects that are understood, managed, and secured at the device level.

Offline storage
Any storage medium that must be inserted into a storage drive by a person before it can be accessed by the computer system is considered to be a type of offline storage. Also called removable storage.

Online data storage
Also called Internet storage or hosted storage, online data storage is a data storage management solution that enables individuals or organizations to store their data on the Internet using a service provider, rather than storing the data locally on a physical disk, such as a hard drive or tape backup.

Open document management API
Open document management API (ODMA) is an open industry standard that enables desktop applications to interface with a document management system (DMS). ODMA simplifies cross-platform and cross-application file communication by standardizing access to document management through an API. ODMA allows multiple applications to access the same DMS without the need for a hard-coded link between the application and the DMS.

Operational data store
A type of database that serves as an interim area for a data warehouse in order to store time-sensitive operational data that can be accessed quickly and efficiently. In contrast to a data warehouse, which contains large amounts of static data, an operational data store contains small amounts of information that is updated through the course of business transactions. An operational data store will perform numerous quick and simple queries on small amounts of data, such as acquiring an account balance or finding the status of a customer order, whereas a data warehouse will perform complex queries on large amounts of data. An operational data store contains only current operational data while a data warehouse contains both current and historical data.

Overwrite(v.)
To record or copy new data over existing data, as in when a file or directory is updated. Data that is overwritten cannot be retrieved.
(n.) Refers to a file or directory that has been overwritten.

Data Storage

Data Backup Glossary (Letter N)

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Near-line storage
Near-line storage is used by corporations, including data warehouses, as an inexpensive, scalable way to store large volumes of data. Near-line storage devices include DAT and DLT tapes (sequential access); optical storage such as CD-ROM, DVD, and Blu-ray; magneto-optical which utilize magnetic heads with an optical reader; and also slower P-ATA and SATA hard disk drives. Retrieval of data is slower than SCSI hard disk which is usually connected directly to servers or in a SAN environment. Near-Line implies that whatever media the information is stored on, it can be accessed via a tape library or some other method electronically as opposed to off-line which signified some human intervention is required, such as retrieving and mounting a tape. Near-line can be slower, but the type of data (historical archives, backup data, video, and others) dictates that the information will not require instant access and high throughput that SAN and SCSI can provide and is less expensive per byte.

Network-attached storage(NAS)
A network-attached storage (NAS) device is a server that is dedicated to nothing more than file sharing. NAS does not provide any of the activities that a server in a server-centric system typically provides, such as e-mail, authentication, or file management. NAS allows more hard disk storage space to be added to a network that already utilizes servers without shutting them down for maintenance and upgrades. With a NAS device, storage is not an integral part of the server. Instead, in this storage-centric design, the server still handles all of the processing of data but a NAS device delivers the data to the user. A NAS device does not need to be located within the server but can exist anywhere in a LAN and can be made up of multiple networked NAS devices.

Nyquist’s Law
Also called Nyquist’s Theorem. Before sound as acoustic energy can be manipulated on a computer, it must first be converted to electrical energy (using a transducer such as a microphone) and then transformed through an analog-to-digital converter into a digital representation. This is all accomplished by sampling the continuous input waveform a certain number of times per second. The more often a wave is sampled the more accurate the digital representation. Nyquist’s Law, named in 1933 after scientist Harry Nyquist, states that a sound must be sampled at least twice its highest analog frequency in order to extract all of the information from the bandwidth and accurately represent the original acoustic energy. Sampling at slightly more than twice the frequency will make up for imprecisions in filters and other components used for the conversion.

Data Storage

Data Backup Glossary (Letter M)

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Magnetic drum
A direct-access, or random-access, storage device. A magnetic drum, also referred to as drum, is a metal cylinder coated with magnetic iron-oxide material on which data and programs can be stored. Magnetic drums were once used as a primary storage device but have since been implemented as auxiliary storage devices.

Magneto-optical
Magneto-optical (MO) is a type of data storage technology that combines magnetic disk technologies with optical technologies, such as those used in CD-ROMs. Like magnetic disks, MO disks can be read and written to. And like floppy disks, they are removable. However, their storage capacity can be more than 200 megabytes, much greater than magnetic floppies. In terms of data access speed, Mo disks are faster than floppies but not as fast as hard disk drives.

Mass storage
The various techniques and devices for storing large amounts of data. Modern mass storage devices include all types of disk drives and tape drives. Mass storage is distinct from memory, which refers to temporary storage areas within the computer. Unlike main memory, mass storage devices retain data even when the computer is turned off.

Massive array of idle disks
In storage terminology a massive array of idle disks (MAID) is a technology that uses a large group of hard disk drives (hundreds or even thousands), with only those drives that are needed actively spinning at any given time. MAID is a storage system solution that reduces both wear on the drives and also reduces power consumption. Because only specific disks spin at a given time, what is not in use is literally a massive array of idle disks, which also means the system produces less heat than other large storage systems.

Mean time to repair
In data storage, mean time to repair (MTTR) is the average time before an electronic component can be expected to require repair.

Mean time until data loss
In data storage, mean time until data loss (MTDL) is the average time until a component failure can be expected to cause data loss.

Media
Plural of medium.

Objects on which data can be stored. These include hard disks, floppy disks, CD-ROMs, and tapes.

In computer networks, media refers to the cables linking workstations together. There are many different types of transmission media, the most popular being twisted-pair wire (normal electrical wire), coaxial cable (the type of cable used for cable television), and fiber optic cable (cables made out of glass).

The form and technology used to communicate information. Multimedia presentations, for example, combine sound, pictures, and videos, all of which are different types of media.

Metadata catalog service
Metadata catalog service (MCS) is a mechanism for storing and accessing descriptive metadata and allows users to query for data items based on desired attributes. MCS may be used for storing and accessing metadata about logical files.

Mixed platform environment
A heterogeneous environment that includes multiple platform types.

Mount
In the network file system (NFS), a protocol and set of procedures to specify a remote host and file system or directory to be accessed, and their location in the local directory hierarchy.

ms, MS
When spelled ms, short for millisecond, one thousandth of a second. Access times of mass storage devices are often measured in milliseconds.
When spelled MS, short for Microsoft or mobile subscribers.

Multi-platform
See heterogeneous environment.

Multi-site
Geographically dispersed; having more than one location.

Data Storage

Data Backup Glossary (Letter L)

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Light archive
In reference to data storage, an archive that can be accessed by many authorized users. Access to the data is open to all the members of the “community” that have a need for the data.

Lightbox
In digital asset management (DAM) systems, an area within the web site (or web service) or other internal DAM where users can create and store a list of assets they want to reference or use at a later time. Lightboxes are common on stock photo web sites where registered users can store images until they are ready to download them.

Linear tape open
Linear tape open (LTO) is a technology that was developed jointly by HP, IBM, and Certance (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 have multiple sources of product and media. The open nature of the technology also provides a means of enabling compatibility between different vendors’ offerings.

Local area network
A local area network (LAN) is a communications infrastructure—typically Ethernet—designed to use dedicated wiring over a limited distance (typically a diameter of less than five kilometers) to connect a large number of intercommunicating nodes.

Lost cluster
Also called a lost allocation unit, or a lost file fragment. A data fragment that does not belong to any file, according to the system’s file management system, and, therefore, is not associated with a file name in the file allocation table. Lost clusters can result from files not being closed properly, from shutting down a computer without first closing an application, or from ejecting a storage medium, such as a floppy disk, from the disk drive while the drive is reading or writing.

Low-level format
(n.) A formatting method that creates the tracks and sectors on a hard disk. Low-level formatting creates the physical format that dictates where data is stored on the disk. Modern hard drives are low-level formatted at the factory for the life of the drive. A PC cannot perform an LLF on a modern IDE/ATA or SCSI hard disk, and doing so would destroy the hard disk. A low-level format is also called a physical format.

(v.) The process of performing low-level formatting.

Data Storage

Data Backup Glossary (Letter I)

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iFCP
The Internet Fibre Channel Protocol (iFCP) allows an organization to extend Fibre Channel storage networks over the Internet by using TCP/IP. TCP is responsible for managing congestion control as well as error detection and recovery services. iFCP allows an organization to create an IP SAN fabric that minimizes the Fibre Channel fabric component and maximizes use of the company’s TCP/IP infrastructure.

Image

In computer science an image is an exact replica of the contents of a storage device (a hard disk drive or CD-ROM for example) stored on a second storage device.
Often used in place of the term digital image, which is an optically formed duplicate or other reproduction of an object formed by a lens or mirror.

Incremental backup
Any backup in which only the data objects that have been modified since the time of some previous backup are copied. Incremental backup is a collective term for cumulative incremental backups and differential incremental backups. Contrast with an archival, or full, backup, in which all files are backed up regardless of whether they have been modified since the last backup.

Information classification and management
Information classification and management (ICM) is a class of application-independent software that use advanced indexing, classification, policy and data access capabilities to automate data management activities above the storage layer.

Infrastructure
The combined set of hardware, software, networks, facilities, and other components (including all of the information technology) necessary to develop, test, deliver, monitor, control, or support IT services. Associated people, processes, and documentation are not part of an infrastructure.

Intelligent information management
Intelligent information management (IIM) is a set of processes and underlying technology solutions that enables organizations to understand, organize, and manage all sorts of data types (for example, general files, databases, and e-mails). Key attributes that define an IIM solution include the following:

Interrecord gap
The space between two consecutive physical blocks on a data recording medium, such as a hard drive or a magnetic tape. Interrecord gaps are used as markers for the end of data and also as safety margins for data overwrites. An interrecord gap is also referred to as an interblock gap.

Internet small computer systems interface
Internet small computer systems interface (iSCSI) is a transport protocol that enables the SCSI protocol to be carried over a TCP-based IP network. iSCSI was standardized by the Internet Engineering Task Force and described in RFC 3720.

IP storage
A technology being standardized under the IP Storage (IPS) IETF Working Group. Same as SoIP.

Data Storage

Data Backup Glossary (Letter H)

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Heterogeneous environment
An IT environment that includes computers, operating systems, platforms, databases, applications, and other components from different vendors.

Hierarchical storage management
Hierarchical storage management (HSM) is a data storage system that automatically moves data between high-cost and low-cost storage media. HSM systems exist because high-speed storage devices, such as hard disk drives, are more expensive (per byte stored) than slower devices, such as optical discs and magnetic tape drives. While it would be ideal to have all data available on high-speed devices all the time, this is prohibitively expensive for many organizations. Instead, HSM systems store the bulk of the enterprise’s data on slower devices, and then copy data to faster disk drives when needed. In effect, HSM turns the fast disk drives into caches for the slower mass storage devices. The HSM system monitors the way data is used and makes best guesses as to which data can safely be moved to slower devices and which data should stay on the hard disks.

High availability
The availability of resources in a computer system in the wake of component failures in the system. High availability can be achieved in a variety of ways—from solutions that use custom and redundant hardware to ensure availability to solutions that provide software solutions using off-the-shelf hardware components. The former class of solutions provides a higher degree of availability, but is significantly more expensive than the latter class. This high cost has led to the popularity of the latter class, with almost all vendors of computer systems offering various high availability products. Typically, these products survive single points of failure in the system.

High-level format
(n.) A formatting method that initializes portions of the hard disk and creates the file system structures on the disk, such as the master boot record and the file allocation tables. High-level formatting is typically done to erase the hard disk and reinstall the operating system back onto the disk drive.

(v.) The process of performing high-level formatting.

Holographic data storage
A mass storage technology that uses three-dimensional holographic images to enable more information to be stored in a much smaller space. In holographic storage, at the point where the reference beam and the data carrying signal beam intersect, the hologram is recorded in the light sensitive storage medium.

Hosted service
A service in which day-to-day related management responsibilities are transferred to the service provider. The person or organization that owns or has direct oversight of the organization or system being managed is referred to as the offerer, client, or customer. The person or organization that accepts and provides the hosted service is regarded as the service provider. Typically, the offerer remains accountable for the functionality and performance of a hosted service and does not relinquish the overall management responsibility of the organization or system.

Hot backup
A technique used in data storage and backup that enables a system to perform a routine backup of data, even if the data is being accessed by a user. Hot backups are a popular backup solution for multi-user systems as no downtime to perform the backup is required. If a user alters the data during the backup process (for example, makes changes at the exact moment the backup system is processing that data) the final version of the backup may not reflect those changes. Hot backup may also be called a dynamic backup or active backup.

Hot potato routing
A form of routing in which the nodes of a network have no buffer to store packets in before they are moved on to their final predetermined destination. In normal routing situations, when multiple packets contend for a single outgoing channel, packets that are not buffered are dropped to avoid congestion. But in hot potato routing, each packet that is routed is constantly transferred until it reaches its final destination because the individual communication links cannot support more than one packet at a time. The packet is bounced around like a “hot potato,” sometimes moving further away from its destination because it has to keep moving through the network. This technique allows multiple packets to reach their destinations without being dropped.

Hot standby
A method of redundancy in which the primary and secondary (backup) systems run simultaneously. The data is mirrored to the secondary server in real time so that both systems contain identical information.

Data Storage

Data Backup Glossary (Letter G)

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Ghost imaging
Using ghosting software, a method of converting the contents of a hard drive—including its configuration settings and applications—into an image, and then storing the image on a server or burning it onto a CD. When contents of the hard drive are needed again, ghosting software converts the image back to original form. Companies often use ghost imaging when they want to create identical configurations and install the same software on numerous machines.

Gigabyte
2 to the 30th power (1,073,741,824) bytes. One gigabyte is equal to 1,024 megabytes. Gigabyte is often abbreviated as G or GB.

Giant magnetoresistive
Giant magnetoresistive (GMR) is a hard disk drive storage technology. The technology is named for the giant magnetoresistive effect, first discovered in the late 1980s. While working with large magnetic fields and thin layers of magnetic materials, researchers noticed very large resistance changes when these materials were subjected to magnetic fields. Disk drives that are based on GMR head technology use these properties to help control a sensor that responds to very small rotations on the disk. The magnetic rotation yields a very large change in sensor resistance, which in turn provides a signal that can be picked up by the electric circuits in the drive.