IBM Z/OS supports it. You'd try to open a file and it would pop up a "retrieving" message and you'd know you could go and get a cup of coffee while you waited f

IBM Z/OS supports it. You'd try to open a file and it would pop up a "retrieving" message and you'd know you could go and get a cup of coffee while you waited for your file. (That's obviously at the OS layer rather than the filesystem layer. But the application didn't know where the file was until it asked for it.)