First of all, are there two physical drives in the computer, or is there a single drive with two partitiions?

If the former, I would pull out the USB drives (temporarily), but my upgrade to Windows 10 went fine with multiple (3) internal drives. If you are worried, I would just open the computer case and just disconnect the drive data cable to the second drive, do the upgrade, then reconnect the drive and Windows 10 should read the second drive just fine.

If the latter, the key is to make sure you only upgrade the system partition, not the entire drive. There are tools available if you need to change the size of partitions to accommodate the new operating system.

Are you looking to do an in-place upgrade or clean install. Either way, it should work fine with multiple drives, at least in general (everyone's situation is different).

Start off with a good backup, maybe even a system image backup. That way you can always quickly get back to where you started.

John

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