OVA export from VMware Cloud Director fails to initiate download after long preparation time for large Virtual Machines

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VMware Cloud Director

When downloading a large Virtual Machine or vApp (e.g., > 1 TB) as an OVA in VMware Cloud Director (VCD), the following symptoms may occur:

The VCD task "Enabling download of Virtual Application" completes with a "Succeeded" status.
No download prompt appears in the web browser, and no file is saved to the client machine.

VMware Cloud Director 10.x

This issue is caused by the expiration of the user's web session during the OVF staging phase.

VCD first transfers the VM data from vCenter to the VCD Transfer Storage (NFS).
For large VMs, this can take several hours.
During this time, the web browser session may reach its Idle session timeout or Maximum session timeout.
Once the staging is complete, VCD attempts to trigger the browser download.
However, because the session has already expired, the browser cannot authenticate the download request, and the process fails silently.

To resolve this issue, use one of the following methods:

Adjust Idle Session Timeout
Increase the Web Console "Idle Session Timeout" to a value that covers the time required for the "Enabling download" task plus an additional 1 to 2 hours of buffer.
This ensures the session remains active until the preparation phase is complete, allowing the automatic download to trigger successfully.
Adjust Transfer Session Timeout
Extend the "Transfer Session Timeout" to increase the grace period for keeping the staged OVA files on the Transfer Storage.
This allows users more time to manually re-initiate the download if the browser session has already expired.

Note: Extending this value for large files may lead to high disk space consumption on the Transfer Storage.
Manual Session Maintenance
Periodically interact with the web browser (e.g., clicking within the UI) during the preparation phase to prevent the idle session timeout from triggering.
While effective, this may be impractical for tasks that require a long duration.
Re-download after Preparation Completion
If the "Enabling download" task is "Successful" but no download started, the OVA file is already staged on the Transfer Storage.
If you re-run the OVA "Download" within the transfer session timeout period (default: 1 hour), the download will start immediately without repeating the lengthy preparation phase.

Refer to the following document for instructions on how to change the timeout value.

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