You are talking about something that normally would be handled at the operating system level, not the application level, so there's nothing special you need to do in XenForo to be able to write to whatever mount point you have on your server. For example maybe you use
Gluster to spread data around multiple servers for both sharding and redundancy. But you don't need to somehow set that up or configure it in XenForo to use it since the application is just reading/writing to the filesystem as far as it's concerned.