What's the best method to save the player's data to the server?

Method to store the game saves
Which one of the following method should I use ?

• Using a database structure(e.g.. mySQL) to store the game data as blobs?
• Using the server hard disk to store the saved game data as binary data files?

Method to send saved game data to server
What method should I use ?

• socketIO
• web socket
• a web-based scripting language to receive the game data as binary? for example, a php script to handle binary data and save it to file

Meta-data
I read that some games store saved game meta-data in database structures. What kind of meta data is useful to store?