Some time ago I upgraded the hard drive on my macbook to a bigger one, creating a image of the old one and dumping on the new one. Everything worked fine, except it took a long time to actually start the booting process.

Today I found a solution for it: go into System Preferences -> Startup Disk, then choose the harddrive and click restart. This worked out for me, as now it starts booting from the hard drive immediately after I power the machine on.