linux box HDD size question

[M E Fieu]

Hi.. May I know how to check a size of the HDD (s) in a linux box. If I issued the following
command, does it mean the total HDD size is 30G ??  Could it be some of the HDD space is not used
??  If yes, how to check the real disk space??  Besides, how do we check what is the RAID type and
how many HDD is beside the box via linux command or other mean ?

[root at linux root]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda3             4.0G  289M  3.5G   8% /
/dev/sda9             6.6G  1.9G  4.5G  30% /apps
/dev/sda1             250M   45M  193M  19% /boot
/dev/sda6             5.0G  1.7G  3.1G  36% /home
none                  1.3G     0  1.3G   0% /dev/shm
/dev/sda8             2.0G   83M  1.8G   5% /tmp
/dev/sda7             4.0G  3.1G  712M  82% /usr
/dev/sda5             6.9G  157M  6.4G   3% /var

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