What is the recommended solution to ensure quick access to shared files on a file server if a branch office becomes inaccessible?

Utilizing an Azure file share in conjunction with Azure File Sync is an effective solution to ensure quick access to shared files in scenarios where a branch office becomes inaccessible. Azure file shares provide a managed file storage solution in the cloud that can be accessed from anywhere, while Azure File Sync enables the synchronization of these file shares with on-premises servers, facilitating local access to files.

This combination offers a seamless way to maintain the availability of shared files. In the event that a branch office loses connectivity, users can still access their files stored in the Azure file share without significant delays since the data is readily available in the cloud. Additionally, Azure File Sync maintains a local cache of frequently accessed files, improving performance and user experience.

In contrast, the other options primarily focus on backup solutions rather than direct accessibility. For example, using a Recovery Services vault and Windows Server Backup, or Azure Backup targets data protection and recovery rather than ensuring live, immediate access to files during outages or connectivity issues. Thus, while these may serve well in restoring data post-incident, they do not address the requirement for immediate access in real-time. Therefore, for maintaining file accessibility in a scenario where a branch office is inaccessible, the first option stands out as the most effective solution.