Since RPI has a limited storage, we link it with the NAS (MyLiveBook Duo Live in this experiment). When linking NAS with the RPI, we first tried SAMBA connection that NAS natively supports but found many problems like permission or symbolic linking within a link. So we decided to use the mounting method through FTP (Not SFTP due to the speed problem) using curlftpfs. Details on the final configuration will be recorded later.
Additional tips when reading USB sticks (ex. camera memory card), then check out this page http://elinux.org/RPi_Adding_USB_Drives