I formatted my 2TB drive with ext3 file system, then realised it was a bad idea. Since ext3 and ext4 is a journaling filesystem, there is a strange activity in every 5-10 seconds, making it impossible to spin down the hard drive when not in use. To turn an ext3 file system to ext2, I simply did this:
tune2fs -O ^has_journal /dev/sda1
at terminal after unmounted the drive first.
The description of the -O switch from the man page:
This will make the ext3 filesystem to ext2 (non journalling ext3) in around 10 minutes.
Then I set the suspend timeout to 180s:
hdparm -S 180 /dev/sda
Now the drive spins down during the night and keep warm when needed, because Samba is continuously reading the mounted network shares.