It depends, what you exactly want: idle or standby.
If you set the disk to spindown automaticly, they normaly go into active/idle state, but "not" into standby.
I dont know, if you want to sleep your server but if yes, then you need the standby-state - if the disks are in idle-state, the server will never go to sleep.
You can put all your disks directly to standby-state with this command:
hdparm -y $(ls /dev/sd*|grep "[a-z]$") >/dev/null 2>&1