Anyone trying to plug a USB HDD into the N900 USB ports are wasting their time! This is due to most smaller, 2.5" HDD only use a single cable for both power and data. If you have a device with separate power and data cables (Qty 2 USB plugs) you need to use external power from another source.
I have made a small study using my multiple USB HDDS. During this study I have found that heavy HDD activity causes excessive power consumption above the datasheet (35 watts) and this resulted in nothing but problems when transferring data.
By plugging in any of my USB 2.0 and 3.0 HDD’s I exceeded the total power consumption stated in the WD data sheet. After heavy usage (Win 7 Backups) the router fell over dead and locked up. The lock ups were various, different scenarios that all resulted in a loss of HDD network share and locked out of the HTTP admin console. After rebooting and removing the HDD I can complete 3 win 7 backups at the same time, across the N900 router going to a networked drive attached to a PC.
Previously others have complained about the N900 locking up due to heavy activity, it has nothing to do with the routing/switching of the router. It has to do with power supply and lower rail volts internally when using an attached drive.
I have a USB printer attached and this does not cause any problems as the printer sources its own power, and the USB is only data transfer. Any HDD attached usually consumes more power than the router itself under certain scenarios. WD should either admit this problem, or increase their power supply capabilities. I have not read anywhere in a manual that mentions using externally powered drives only. There is a large percentage of drives sold today that are single cable/port types, rendering them useless for such an application. I do not have any devices with twin ports to try. It would be interesting to hear feedback from users using externally powered drives.