How to set up an iMac not to look for USB Flash drive info during boot up? Short question: is there a way to disable an iMac's USB Flash Drive boot up so that boot up time is faster?



Details:

My iMac has an external USB hub, and it has 3, 4 or sometimes 6 or 7 USB Flash drives plugged into the hub.  But during the boot up of the iMac, there seems to be 20 seconds or 25 seconds before the spinning wheel of the Boot up screen shows up.  During this 20 to 25 seconds, the light of the USB Flash drives can blink for several times.

If I unplug all those USB drives, then the boot up is faster.

Is there a way to tell the iMac not to look for the USB Flash drive info during boot up time?  Maybe it was trying to see if those drives contain any bootable image...  I already set in the System Preference to boot up from the Hard Drive, so maybe there needs to be some extra setting to tell the iMac not to look for any boot info in the USB Flash drive -- is there any way to do that?
Interesting question, but I assume there is no way you can disable the "probing" of attached USB devices on startup. After all, the system has to find out about the characteristics of attached devices, be it sound in/outputs, keyboards, mice or mass storage devices.