I agree with thewebedge. Here is was cpanel suggests:
Partition Size Partition Contents
/boot 70 Megabytes (MB) Kernels, bootloader configuration file.
/usr 8+ Gigabytes (GB) cPanel, Apache, Apache logs, and most applications.
/var 8 + Gigabytes (GB) MySQL databases, cPanel configuration, system logs, and mail queue.
/home Fill to disk All cPanel user accounts.
/tmp 1 Gigabyte (GB) Temporary files.
swap 2x memory (RAM) Overflow from RAM contained on your disk.
I would also suggest you make /tmp no-exec
Driving The Web Further