General :: Make PHP Script Use The Second Hard-disk?

I have two SATA hard-disk drives attached to my server as shown in the following :

[root@cl-185 /]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 222G 166G 45G 79% /
tmpfs 2.0G 0 2.0G 0% /dev/shm
[root@cl-185 /]# fdisk -l | grep Disk
Disk /dev/sda: 250.0 GB, 250000000000 bytes
Disk /dev/sdb: 2000.3 GB, 2000398934016 bytes

Now, being a linux noob I need help on two questions :

1). Why only 'sda1' is shown when using df -h to get disk space usage, and what else needs to be done to check stats for 'sdb' ?

2). My PHP script needs to save a lot of 'cache' files, how to make the script use the second disk for saving the files - I mean what path should I edit in my script (current is '/var/www/html/tmp')