I want to use my Raspberry Pi model B as a NAS, but I'd like to avoid using a USB hub. I have a 2.5" Western Digital 1 TB USB hard disk drive (this one), and a 2 A power supply for the Raspberry Pi that I'm planning on using with it.
Will this work? Could the Raspberry Pi power this hard disk drive, if I connect only one hard disk drive and nothing else?
These type of enclosed hard drives conform to the USB specification 2.0 specification, even though it's USB 3.0 it must be able to fall-back. USB 3.0 provides lots more power, but since it falls back it must conform to the USB 2.0 500 mA maximum current. The hard drive itself might use more power, but the built-in electronics will detect when to use staggered spin up (takes longer to spin up basically)
The inrush current must not exceed 500 mA either; this is when you plug it in, and it spins up. The 3.5" versions draw much more current on spin up since they always need a dedicated power supply and do not need to conform to the USB specification. That is why it's important to use at least a 1.5 A power supply. The Raspberry Pi can use 800 mA at peak times on its own. So if you have Wi-Fi maybe it's good to use 2 A or 3 A power supplies.
The Raspberry Pi was built to the USB 2.0 specification, but unfortunately due to hardware problems the Raspberry Pi resets itself (brown out) when it needs to provide the 500 mA inrush current because of poly fuse and voltage regulator problems or rubbish power supplies that cannot provide the peak current in time. The newest Revision 3, B+ or 2 do not have this problem and this USB hard disk drive will run without any problem.
To get it working on older Raspberry Pi's you either have to bridge the polyfuse or solder +5 directly to the +5 V USB pins.
I have used a few USB hard disk drives on older revisions using the workaround and it's stable.
The hard disk drive used in that enclosure is WDBUZG0010BBK.
From my personal experience, WD Blue HDD (WD10JPVT/WD10JPVX with 0.55A average current) might work more or less reliably (== require about 1 reboot / month) connected directly to RPi without any powered hub.
Your particular HDD requires much higher currents, so it's very unlikely you'll be able to do anything reasonable without an external power.
If your HDD does not have its own power source (excluding USB), it will generate a problem.
For a RPi B, all power that will be drawn by USB port will pass through the main regulator. It is a linear regulator, this part will heat and might overheat when working. RPi B USB ports are not intended/designed to power high-load devices.
The Raspberry Pi delivers power to the USB ports directly from its input jack, not via any circuitry inside the computer. Therefore, providing you can find a 5 V power adapter that can supply enough current to run the combination of the drive and the Raspberry Pi, you should have no issues.
I powered a Raspberry Pi with a gaming grade keyboard rated for 1.0 A with a 2.1 A Nexus Charger without any negative side effects.
It is also worth considering that if the drive has a dual USB connector (a second connector just for power) it may be possible to power the Raspberry Pi and drive from two power adapters.
I've found this article very interesting. The hint from it works well in rpi 2b+ with 5v & 2a support.
My solution to power a WD Elements Portable 3TB drive, is to connect power directly to the GPIO port. In other cases the voltage drop due to a current of about 1A was too much, causing instability. So, use a proper rated wire to connect to the port, a micro USB cable won't do.
