LUN zoning is a method of configuring storage area network (SAN) fabric to match logical unit numbers (LUNs ) so that end device access is limited to the appropriate storage devices. In this context, storage devices are known as logical units.
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The logical unit number (LUN) is a unique identifier used to designate a logical unit, which could be an individual hard disk device or a group of devices. As a rule, end devices, such as hosts, can only see and access storage devices within their own zones. Limiting access in this way improves security and makes it possible to allocate bandwidth by assigning particular ports to a zone. Zoning can be used to isolate a single server to a specific logical unit or associate a group of servers with a logical unit.
In a SAN context, devices requesting input/output (I/O) operations are initiators and the devices that perform these operations are targets. Zoning is configured on a per-target and initiator basis and implemented at the hardware level, for example through a Fibre Channel (FC) switch. When implemented on a port basis, it's known as hard zoning. Soft zoning is implemented through World-Wide Names (WWN). A WWN is a unique identifier that is hard-coded into a Fibre Channel device. Any device with multiple ports has a WWN for each port, which enables more precise targeting.
LUN masking, a further constraint on zoning, subdivides port access so that only LUNs authorized to access a specific server can access the corresponding port.