You can list all the disk in system by following way. Lets have a look,
ls : Show Individual partitions.
# ls /dev/sd* /dev/sda /dev/sda1
ls: just disks, ignore partitions
# ls /dev/sd*[a-z]
/dev/sda
fdisk :
# fdisk -l 2>/dev/null |awk '/^Disk \//{print substr($2,0,length($2)-1)}'
/dev/xvda
These are ways where you will get a list of disk present in your system.