dd if=/dev/sdX bs=4k conv=noerror,sync of=/mount_point_of_extHDD/serverIMG.dd

file serverIMG.dd

mount -o loop,rw,offset=<counted_value_here> -t <partitions_filesystem_type> /mnt/extHDD/serverIMG.dd /mnt/tmp
cat /dev/zero > zeroes.file
rm zeroes.file

VBoxManage convertfromraw serverIMG.dd serverIMG.vhd --format VHD