Você tentou fazer isso, você pode montar o disco rígido para outro, e depois alterar o fstab para montar o diretório para o disco rígido com isso:
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point> <type> <options> <dump> <pass>
/media/disk2/Video /home/vftp/ftp/Movies/ nodev,noexec,nosuid 1
/media/disk4/Anime /home/vftp/ftp/Anime/ nodev,noexec,nosuid 1
/media/Disk4/CartoonSeries/ /home/vftp/ftp/Cartoons/ nodev,noexec,nosuid 1
/media/Disk3/Programs /home/vftp/ftp/Applications/ nodev,noexec,nosuid 1
/media/Disk1/ /home/vftp/ftp/Games/ nodev,noexec,nosuid 1
/media/Disk3/Music/ /home/vftp/ftp/Music/ nodev,noexec,nosuid 1
/media/Disk3/Books/ /home/vftp/ftp/Books/ nodev,noexec,nosuid 1
/media/Disk3/StudyMaterial/ /home/vftp/ftp/StudyMaterial/ nodev,noexec,nosuid 1
# / was on /dev/sda3 during installation
UUID=90f5fb7f-225f-4c4c-8564-b3c2f16f683d /media/Disk1 ext4 error=remount-ro 1
UUID=34a6f835-8ec3-4feb-994d-be669a5ed6cf /media/Disk2 ext4 error=remount-ro 1
UUID=34a6f835-8ec3-4feb-994d-be669a5ed6cf /media/Disk3 ext4 error=remount-ro 1
UUID=f2d0ad61-3a36-4220-9f15-0e11fc4caedc /media/Disk4 ext4 error=remount-ro 1
/home/vftp/ftp/ /home/vftp/kevin/ /media/Disk1 1
/home/vftp/ftp/ /home/vftp/kevin/ /media/Disk2 1
/home/vftp/ftp/ /home/vftp/kevin/ /media/Disk3 1
/home/vftp/ftp/ /home/vftp/kevin/ /media/Disk4 1
e pode funcionar bem assim.