RE: Adding Drives to a T420. Is backplane completely powered? Will the 495W Power Supply be enough?
That would depend on the backplane installed, as the T420 will come with a 8 drive and a 16 drive backplane. From your description I would think that you have trhe 16 drive backplane installed. With all the drives and memory installed, you may push above the capabilities of the 495W power supplies. If there isn't a really large amount of memory, you may not. I couldn't be certain of this without knowing how it is configured and populated. If the power is exceeded the server will notify you via the LCD screen or OpenManage, if it is installed.