Q. How can I create a file server in Azure that is available within a virtual network but not from public endpoints?
A. Azure Storage has support for Azure Files which exposes storage via SMB which is available from virtual networks and from the Internet. If you want a file server that is only available from virtual networks then you should build a file server on IaaS VMs. This could be accomplished in a highly available fashion using Windows Server 2016 and Storage Spaces Direct (SSD) which utilizes local storage on each node. The witness resource could be an Azure Storage account (cloud witness).