service smartd
 

While my machine starts everytime,smartd is taking 2 minutes to on,by default my machine boots with runlevel 5,why its taking too much time to start in 5 ?

Ijust go to runlevel 1 and checked smartd takes 2 seconds to start .

Will I turn off this useful service or what will I do ?

I don't have an advice on why this happens.
But you could overcome this problem while keeping smartd on, by deactivating it, and run it in a different way.
Put an entry
/etc/init.d/smartd start&
(notice the & to have it run in background) in your "/etc/rc.d/boot.local" file. This file is for opensuse, in fedora its path is different, it should be "/etc/rc.d/rc.local"