I recently converted to all Mac operations from Windows, I have installed a drobo with 4 TB. Now the iMac boots in about 4 minutes, I removed the drobo and then the iMac booted in less than a minute. Is the Mac system checking the drives, is that why it takes so long to reboot.
I have read in a couple of other places about Drobos (USB) causing that, but also other USB mass storage devices from iPods and USB drives to flash drives may do the same. It doesn't happen in any pattern, what may work on one won't on another machine. Except for those that tried a different kind of drive I never have heard of a fix though, just read reports that were never followed up.