Glossary D

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data mart
Related to the data warehouse type of application, the data mart is generally designed around a single subject. Consequently, the scope of the information is reduced, along with its relationships, within a greater set of information. For example, a data warehouse application that supports customer financial accounts will have all customers, their accounts, and their related attributes. However, a data mart providing secondary support may only have information that relates to a subset of this information such as customers in a particular region, or a set of financial products and their status. These subset applications are datacentric, and although they utilize a smaller set of data, they remain challenging given their distributed requirements and use of relational databases.
data warehouse
A type of application that allows end users to analyze historical information on a set of related subjects. For example, a data warehouse for a financial application may have information for the past three years on all customers, their accounts, and any related attributes. Therefore, using relation data base technology, an end user can query all customers in a particular set of states that have moved within the last year and have brokerage accounts. These applications are datacentric and can be the largest users of both storage and processing capacity within a data center.
Digital Linear Tape (DLT)
A format for magnetic tape that has become an ad hoc standard for open systems. The architecture is based on the DLZ1, a special compression algorithm where data is written on the tape in dozens of straight-line (linear) tracks, usually 128 or 208. Capacities are vendor-dependent but range to >>50GB of data when compression is used. A variant of DLT technology, Super DLT, provides capacities to move beyond the 100GB on a single cartridge.
Direct Access File System (DAFs)
A file system used specifically with NAS devices, where file access bypasses the normal file location services through the OS and storage controllers and utilizes a new service called virtual interface (VI). This allows files to be transferred through direct-memory transfers, which circumvent the overhead of TCP processing for file access. This, however, requires that a number of new components be implemented, including a new type of network card which enables the VI protocols and NAS devices that process direct memory addressing.
A class of storage switching devices that are generally defined as having the attributes of >>64 ports, additional hardware functions that enable redundancy within the switch, and related software that configures recovery and redundancy features.
disk compression
Operations that allow data on a disk to be compressed for efficiency of space utilization. Compression algorithms usually find all spaces and duplicate characters and remove these from the storage data source. These are then replaced when the data is accessed.
disk defragmentation
Disks read and write information in a random manner, which is part of their value in accessing data. However, as write operations occur over time, the disk becomes fragmented as the drive writes related data blocks out to available blocks, clusters, or sectors, depending on the type of disk device and operating environment. This fragmentation of the disk, with related data spaced all over the geometry of the drive, begins to cause performance problems since it takes the disk head longer to read the segments of the file, or find available space within a fragmented disk. Defragmentation, sometimes referred to as defragging, moves all the scattered blocks, clusters, or sectors into a contiguous space on the drive, essentially reorganizing the drive so it can operate more efficiently .
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Storage Networks
Storage Networks: The Complete Reference
ISBN: 0072224762
EAN: 2147483647
Year: 2003
Pages: 192 © 2008-2017.
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