flyingcircus

No its not the safe side... If the usb HDD runs in low voltage and its slow.. then maybe you wont have any problem. But in most cases, you will... The hdd will try to drain more power to work and it will stop working due to limited usb power. Then the hdd will reset and restart and anything you did before, will be lost.

oh come on seriously? the amount of half knowledge hidden in this sentence is baffling
i actually felt coerced to sign up just because of that

2.5" hard drives are designed to work with less power than they might need, this is the only reason why they can be powered with usb only at all and it is also a requirement to work without interruptions in a notebook that runs on battery power
if the drive absolutely needs more power than usb 2.0 can deliver it will ship with a y-cable so you can connect it to both usb ports (usually the case with 7200 rpm drives.. 5400 rpm drives will usually work with a single usb connector however i've been using my wii with a 2.5" 7200rpm internal HDD in external casing, meaning it was not specifically meant as an external HDD, for years without ever running into trouble)

if they draw more than usb 2.0 can give but still receive enough to continue operation the result is that they will slow down, which will of course affect file transfer speeds and reaction time however NO files will be lost even if the hard drive should "restart" (which it won't)
your files are absolutely safe when plugging in a 2.5" drive on a single connector as is your console
usb will never deliver more power than it is specified for (standard is 2.5watts)
if the usb port can't deliver the necessary power it will simply not start up

if the engineers at nintendo are worth their salt they'll also have designed the PSU of the wii-u so that it will be able to power all usb ports, render a demanding game and power any additional peripherals at the same time without running outside specifications

They could avoid that, by adding a high voltage usb port.. those usb ports we use for recharging and transfer data as well, they can give extra power for this hdds and they cost nothing!!  I wonder why they didnt do that... Or they could add a docking station, attached on wii U, with e-sata port connector.

there is NO such thing as a high voltage usb port
every port MUST run at 5V it's in the specification.. if an unaware user was to plug his usb device into a usb port that delivers more than 5V he'd have to buy a new device
you're probably referring to usb 3.0 since it delivers a higher current than usb 2.0.. voltage is the same

ps: if you search almost 1 year ago messages in here.. you will find one post of mine, talking about it...  And I know this problem from the PC... it was a huge problem before they release the high voltage usb ports... Usb hdd's crashed all the time because of it. Thats how I knew that this is a small conflict with wii U. They dont crash in a small file transfer (saves or small reads, downloads).. but they do crash in a huge file transfer.. eg. Game installment, a game that runs entirely from the usb hdd and the hdd works very intensively....

i've never heard of these stories you're talking about.. if a 2.5" drive is specified as an external usb 2.0 drive it will definitely run on any standard usb 2.0 port, also i have been running plenty of games off several different external 2.5" usb HDD with no problems whatsoever

This can lead to burning out the PSU, and lead to overheating.  This is no different than a PC trying to run a video card that requires a larger PSU.  It will still power the card, but in time, it could cause damage.

actually any decent PSU will rather either shut down completely or choke the power delivered to the PC (potentially causing it to crash which will however not hurt the hardware of the PC) before the PSU itself is damaged
anywho
there is a fixed number of connectors on the wii-u.. if the PSU isn't capable of powering all of them at the same time then something went horribly wrong during the design of the console
besides the 2.5 watts are delivered directly to the device on the usb port.. there will be no additional heat generated inside the console.. the only additional heat would be generated in the PSU itself which is not inside the console and should, as already mentioned, be capable of dealing with the load

I am not saying this WILL happen.  But telling someone they have nothing to worry about, is simply giving false information.

no the information that has been given is completely correct
it is save

There is always a possibility of running in to risks when you use an external hard drive running off of the consoles PSU.  Most consoles have amperage designed for that console to run properly.  Taking away from that could lead to issues.

i see so the external HDD drawing the same power from 2 usb connectors is alright (as confirmed by nintendo) but when drawing from one usb connector it magically damages the console (and no the usb connector cannot deliver more power than it's specified for in case you'd like to bring that up)
you should probably reflect on that some more because it makes no sense at all