You are installing an OS remotely using Virtual Media In IDRAC.

The Integrated Dell Remote Access Controller (iDRAC) Virtual Media feature allows an administrative workstation to map local or network-attached disk images directly to the host server as virtual USB storage components. However, when the console client reports that "Virtual media is currently unavailable," it indicates an active session contention policy enforcement within the out-of-band controller subsystem. This state typically occurs when a remote network file share session—such as a concurrent ISO mount via an explicit CIFS, NFS, or HTTP/HTTPS configuration path—is already bound to the virtualization engine. The underlying architecture restricts simultaneous file mapping sources to prevent data stream collision and drive mapping conflicts at the boot manager layer. To restore client-side interactive Virtual Media functionality, any pre-existing background server-side network mount mappings must be explicitly unmounted or disconnected. Once the background storage pipeline is cleared, the controller frees the virtual device manager lock, allowing the administrator to successfully establish a new client-based media redirect session.

Study Guide References: Troubleshooting; Virtual Media Subsystems; iDRAC Remote Management Session Policies.