One challenge with writes in the middle is that it changes the file hash. Cloud services typically expose the object hash, so changing any bit of a 1TB file would require a costly read of the whole object to compute the new hash.
You could spilt the file into smaller chunks and reassemble at the application layer. That way you limit the cost of changing any byte to the chunk size.
That could also support inserting or removing a byte. You'd have a new chunk of DEFUALT_CHUNK_SIZE+1 (or -1). Split and merge chunks when they get too large or small.
Of course at some point if you are using a file metaphor you want a real file system.
You could spilt the file into smaller chunks and reassemble at the application layer. That way you limit the cost of changing any byte to the chunk size.
That could also support inserting or removing a byte. You'd have a new chunk of DEFUALT_CHUNK_SIZE+1 (or -1). Split and merge chunks when they get too large or small.
Of course at some point if you are using a file metaphor you want a real file system.