What Is a Storage LUN?
Organizations that produce large amounts of data often use a separate computer network for storage purposes. These storage area networks, or SANs, typically contain multiple devices for storing electronic documents. These systems use a Logical Unit Number, or LUN, scheme for identifying the various devices that comprise the storage network. The LUN system allows administrators to assign storage access for individual devices within the network.
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Storage Area Network
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A SAN is the entire separate storage system used by an organization. It typically includes host servers, switches and disk-based storage subsystems. The computers used by organization employees connect to the storage subsystems through the switches. The system then uses the storage subsystems to store documents and other data generated by employees. LUN numbers do not apply to every device within a SAN. Rather, LUN numbers exist for devices within a storage subsystem.
SCSI Bus
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A Small Computer System Interface, or SCSI, bus connects devices in a storage area network. The acronym "iSCSI" identifies an Internet Small Computer System Interface, which provides SCSI technology through the Internet. A single SCSI bus consists of up to eight devices. Each device within the bus has its own LUN identification number. The SCSI basic input/output system, or BIOS, assigns a number from "0" to "7" for an 8-bit bus and "0" to "15" for a 16-bit bus.
To use a LUN for storage in an SCSI system, the administrator must first assign a target and a server or cluster of servers. A target is a logical entity that controls the connection between the organization's computer servers and the LUN. A target can control access to up to eight devices. An initiator communicates with the target when a server attempts to store data. Once the target grants access, the server can store data on the LUN.
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Fibre Channel
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Fibre Channel technology is the more recent approach to setting up a SAN. According to TechTarget, Fibre Channel is replacing SCSI because it is three times faster. Devices within a Fibre Channel storage network can also have LUN numbers. The administrator assigns a server or cluster of servers and one or more ports on a host bus adapter to each LUN. There are no targets to assign in a Fibre Channel system.
Data Storage
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Each LUN can act as a physical disk drive for storage purposes. According to Microsoft, a LUN can also be a section of a disk, an entire disk array or an individual section of a disk array. A disk array is a group of two or more disk drives. Users can access the LUN to read and write data.
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References
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