> # Key Concepts

> The following terms are used throughout this chapter:

> - Virtual device—The virtualized or proxy representation of the real device, which is registered with the name server and has a pWWN and FC ID. A virtual device exists as long as its real (physical) counterpart is online. The virtual device pWWN and FC ID must be unique and cannot clash with any real device pWWNs and FC IDs.
> - Virtual domain—Reserved by SDV to assign FC IDs to virtual devices. If the switch that reserved the domain goes down, another switch takes over its role using the same domain.
> - Primary device—The device that is configured as primary. By default, the primary device becomes the active device if it is online.
> - Secondary device—The additional device that is configured. By default, the secondary device is standby.
> - Active device—The device that is currently virtualized is called the active device. By default, the primary device becomes the active device if it is online. The active device is indicated by a (*) symbol.

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