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SQL Server storage system terminology

  • Oct 27 / 2008
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SQL Server storage system terminology

While going through literature about storage systems for SQL Server, a Database Administrator (DBA) may come across to several terms of storage system. Database Administrator (DBA) may have a better grasp of under sight help if some related basic terminology of storage system is known. Following are some terms used in storage systems for SQL Server

Direct attached storage (DAS)

Direct-attached storage (DAS) is computer storage that is directly attached to one computer or server and is not, without special support, directly accessible to other ones. Direct attached storage (DAS) utilizes any storage system that is not part of network. Storage device is directly attached to host. The storage may be external or internal but not the network storage. The main protocols used in Direct attached storage (DAS) are SCSI, SAS, and Fibre Channel. A Direct attached storage (DAS) system enables storage capacity extension for a server. The interface with the server or the workstation is made through a host bus adapter (HBA).

Direct attached storage (DAS)
Direct attached storage (DAS) systems are most often made of an enclosure without active components such as controllers, thus access logic and fault tolerance patterns are provided by the server HBA. Middle and top range DAS systems provide embedded controllers. DAS controllers also enable shared storage access, which permits multiple servers (usually no more than 4) to access the same logical storage unit.

Network attached storage (NAS)
Network attached storage (NAS) is hard disk storage that is with its own network address. Network attached storage (NAS) is not attached to the department computer that is serving applications to a network’s workstation users. So, both application programming and files can be served faster because they are not competing for the same resources. Network attached storage (NAS) device is attached to a local area network. Network attached storage (NAS) is available to server/host via IP and LAN. A NAS unit is self-contained computer connected to a network. Sole purpose of Network attached storage (NAS) is to provide file-based data storage services to other devices on the network. The operating system and other software on the Network attached storage (NAS) unit provide the functionality of data storage, file systems, and access to files, and the management of these functionalities. Although Network attached storage (NAS) is not designed to carry out general-purpose computing tasks but other software may be run on it.

Storage Area Network (SAN)

A storage area network (SAN) is a high-speed special-purpose network or sub network that interconnects different kinds of data storage devices with associated data servers. Typically, a storage area network (SAN) is part of the overall network of computing resources for an enterprise. Storage Area Network (SAN) allows a network of systems to access the storage over a dedicated storage network. Dedicated network may be an IP network (iSCSI SAN) or a fibre channel network (FC SAN). Storage Area Network (SAN) is architecture to attach remote computer storage devices (such as disk arrays, tape libraries and optical jukeboxes) to servers in such a way that, to the operating system, the devices appear as locally attached. Storage Area Network (SAN) are still uncommon outside larger enterprises.

Fibre Channel (FC)

Fibre Channel (FC) is a technology for transmitting data between computer devices at data rates of up to 4 Gbps (and 10 Gbps in the near future). Fibre Channel (FC) is especially suited for connecting computer servers to shared storage devices and for interconnecting storage controllers and drives. As Fibre Channel is three times as fast, it has begun to replace the Small Computer System Interface (SCSI) as the transmission interface between servers and clustered storage devices. Fibre Channel (FC) is a serial data transfer technology. Fibre Channel (FC) provides data transfer facility on very high bandwidth across long distances. Fibre Channel (FC) is a gigabit-speed network technology primarily used for storage networking. It started use primarily in the supercomputer field, but has become the standard connection type for storage area networks (SAN) in enterprise storage. Despite common connotations of its name, Fibre Channel signaling can run on both twisted pair copper wire and fiber-optic cables.

Fibre channel protocol (FCP)
Fibre channel protocol (FCP) maps the SCSI-3 protocol to implement serial SCSI over FC networks. Fibre channel protocol (FCP)transfers data at block level.

Small computer system interface (SCSI)

Small computer system interface (SCSI) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The Small computer system interface (SCSI) standards define commands, protocols, and electrical and optical interfaces. Small computer system interface (SCSI) is a parallel interface standard for attaching peripheral devices to computers. These devices may be storage, printers, tape drives etc.

Internet SCSI (iSCSI)

Internet SCSI (iSCSI) is an IP based standard for linking hosts to storage devices over a network. Data is transported by SCSI commands encapsulated in TCP/IP packets over the network. Internet SCSI (iSCSI) is a protocol that serializes SCSI commands and converts them to TCP/IP

Host bus adapter (HBA)

Host bus adapter (HBA) is mostly referred as I/O adapter card used to connect a host computer to a storage device. Host bus adapter (HBA) performs low level interface functions to minimize the impact on performance of host processor. A host bus adapter (HBA) is a circuit board and/or integrated circuit adapter that provides input/output (I/O) processing and physical connectivity between a server and a storage device. Because the Host bus adapter (HBA) relieves the host microprocessor of both data storage and retrieval tasks, so Host bus adapter (HBA) can improve the server’s performance time. Host bus adapter (HBA) and its associated disk subsystems are sometimes referred to as a disk channel. Host bus adapter (HBA) connects a host system to other network and storage devices.

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