While I dont understand your need to use a fat file system, this seems a duplicate of http://unix.stackexchange.com/a/17173/108069

In your case each of your dd files would be 4gb each.

While I dont understand your need to use a fat file system, this seems a duplicate of https://unix.stackexchange.com/a/17173/108069

In your case each of your dd files would be 4gb each.