Glossary P-Z

P-Z

PCI Bus

A bus system to connect peripheral devices, which has become a standard within the industry. PCI buses provide the interconnections to the internal and external storage devices through adapter connectivity points, but also provide the interconnections between the CPUs, RAM, and caching systems.

Relational Database Management System (RDBMS)

A database system that allows for the organization and access of data using relational operations. RDBMS architectures are developed from tables where entities are defined with each table and attributes are defined as columns or fields within the table. These databases have become the preferred method of storing information for both transactional and analytical systems. RDBMS architectures provide their own file systems and special I/O operations given they are table-driven and have different data access and storage characteristics than file systems.

SCSI

A standard term for a type of bus storage architecture used with block-level devices such as disks and tape. The Small Computer Systems Interface (SCSI) defined the standards used with connecting storage through parallel bus architectures. Forming the largest install base of storage devices today, the SCSI command structure has superseded its bus application and is used with both FC protocols and the newly defined iSCSI standard.

service levels

Service levels exist on several levels. There are specific agreements with end users that define the level of service the IT department provides. Internal service levels are managed to provide a working measurement of systems and networking performance. Service levels for storage, if they exist, are often integrated into the internal system service levels and are comprised only of capacity measurements for end users. The establishment of meaningful measurements for the storage- networking infrastructure that encompasses storage, systems, and network specifications have yet to be developed.

SMP

Symmetrical multiprocessing defines a configuration that provides multiple computing nodes supported by both shared memory and shared I/O configurations. These are generally characterized by multiple CPUs within the same cabinet. The scalability restrictions have long centered on the limitations of the shared I/O structure and related performance problems with storage scalability. SMP configurations are greatly enhanced by the inclusion of storage networks, especially SANs that provide additional bandwidth and speed to the I/O storage subsystem.

snapshot

A term used for copying online data at a synchronized time and providing a copy of a data volume, file system, or database for later access. Used in response to user data requiring 24/7 access, snapshot configurations generally require a duplicate volume to be operating so that the actual copy is made from the duplicate volume. This allows uninterrupted backup operations, and provides a consistent snapshot of the data at the time it was executed. Once the snapshot (backup) is taken, the duplicate volume then resynchronizes itself with the primary online volume and continues processing.

T11.3 standard

The ANSI Fibre Channel standard specifications. All vendors whose products support Fibre Channel work through this set of specifications. The ANSI Fibre Channel X3T11 Committee governs these.

tape compression

A setup of functions and operations that allows data on a tape to be compressed for space efficiency purposes. 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.

temporary storage

These consist of various locations within a computer system where data is stored temporarily until it can be used by the CPU or written on a storage device. These locations are considered internal when described as system cache, CPU registers, and memory buffers in RAM. They are external when considered as part of a peripheral such as a block device.

track

A fundamental measurement of a disk's geometry that spans the circle made by the disk head as it makes a single rotation of the media platter. Track sizes, therefore, are relative to the size and density of the media platter. Tracks are formatted for use with an operating environment by way of the operating system dividing the tracks into clusters or sectors. Tracks aligned vertically with multiple platters make up another measurement called a cylinder.

zones

Functions within a FC switch that allow the ports to be segmented into individual areas for node access. Authorized access lists for each port provides login services to the switched fabric defined zones. Zoning can further be determined regarding the attributes of the ports, node login addresses, and login attributes. This allows the SAN to define access to authorized devices such as servers to attached storage devices such as disk and tape arrays.