Buy Online or Call 1-800-WWW-DELL

Dell SAN Foundations Online Training Course

Previous Next This button takes the user to the next page.

Interface

Fibre Channel Concepts

Topologies

Hardware Components

Environmental Concerns

Software Components

Storage Area Network: Architecture

Switches

In a SAN, Fibre Channel switches (which resemble regular Ethernet switches) are the connection point between servers and storage devices. Fibre Channel switches usually have 8, 16, 32, or 64 ports.

PowerVault 56F Switch Switches are used to provide a point-to-point connection between servers and storage devices. Dell's product offerings include the PowerVault 56F (pictured at left).

SAN Fabric

A fabric is created by a group of interconnected storage devices attached to the switch. Generally a fabric can be thought of as a set of switches sharing Inter-Switch Links (ISLs) together with the devices to which they are connected. Each ISL is considered a hop. A fabric can support multiple hops without performance degradation. Typical installations usually include fewer than seven hops.

Redundant Fabrics

A SAN with multiple switches not connected by ISLs provides multiple fabrics, which in turn can lead to redundancy. Two fabrics in a SAN installation are required to provide redundancy. The redundant fabric's purpose is to provide an alternate path in case the primary fabric in the installation fails. If the redundant fabric is active, it may be providing additional bandwidth when the primary fabric is operational. In this case, the redundant fabric may not be symmetrical and thus may not provide full redundancy.

Zoning

An advantage of Fibre Channel switches is the ability to set up barriers between different devices. These barriers, called zones, create logical boundaries within a fabric; each zone contains selected devices including servers and storage components. Zones can restrict access to a device within a particular zone regardless of proximity. Devices not included in a particular zone are not available to members of that zone.

The graphic (below, right) is a copy of a SAN zoning poster. While the details can't be read, it serves to illustrate the complicated nature of zoning in a SAN.

Zoning is required in heterogeneous SAN configurations to separate incompatible environments such as operating systems. It may be used in other configurations depending on the components and environments specific to your SAN.
Zones can be configured dynamically. The number of zones and zone membership are unlimited. Devices can be members of one or more zones within a fabric. This image shows how a SAN implementation might be zoned

World-Wide Names

World-Wide Names (WWN) are predefined and assigned to certain devices within the SAN such as HBAs, switches, and storage devices. WWNs are unique to each device and are used to support routing of SAN data, zoning, and failover functionality. A WWN consists of an eight-byte hexadecimal number with each byte separated by a colon; for example, 10:00:00:69:00:8a:56:78. A zone alias can be created to simplify zone member entries. The name NT_Server1 could be used as an alias for the WWN 10:00:00:69:00:8a:56:78.

Cascading

Cascading allows multiple switches in the same fabric to be linked together for switch expansion. For example, a 16-port switch can be cascaded to another 16-port switch to create a virtual switch with 32 ports. Cascading is performed automatically when each switch detects an intra-switch ISL. Zone information specific to the fabric is replicated to the new switch.