This example shows the status of a Samsung 1 TB external 2.5" USB hard disk.
all files and folders can be read and written
hardware self tests and Surface test functions from Disk menu shows no problems with the hard disk in general or the hard disk surface
it may take some seconds while the contents of the hard disk is accessible in Windows
Initially, the hard disk health reported is 85 %.
Problems occurred during the spin up of the disk 5 times.
Power on time: 15 days, estimated remaining lifetime: more than 1000 days
As the text description indicates, the problem can be caused by that the hard disk has no enough power to spin up properly. This causes spin retries: during the spin-up procedure, the hard disk tries to reach the designed rotation speed and move the read/write heads from the parking zone / parking ramp over the active hard disk surface. During this operation, the power is insufficient and the result is that both the disk surface and the heads can be damaged as they can't enter correctly to the working or the parking position.
The issue is caused by a design problem: a single USB 1.1/USB 2.0 connector can provide up to 500 mA power which is insufficient for most 2.5" notebook hard disks to spin up and operate properly. Just scroll down to the end of the Information page for your external hard disk, to check the "Required Power For Spinup" value:
Problems are even worse on front panel USB connections. In some situations, the increased power output on these front panels can even damage the external hard disk or the motherboard itself. Some motherboards are protected against this and can provide additional power which may be better to connect external hard disks. USB 3.0 is designed to improve this situation as it can provide up to 900 mA power on a single line. It seems better - however may still not be enough for a larger capacity 2.5" external hard disk.
The solution is to use a double (Y) USB cable, which is connected to 2 USB connections and thus can provide the additional power output of these two slots. Like this one:
Please note that most 2.5" external USB hard disks (from diffrent manufacturers, like Western Digital, Seagate, Samsung, etc...) are shipped with a single USB cable: one end of the cable is connected to the external hard disk and the other is connected to a single USB connection. It is always recommended to replace this cable with a short, Y USB cable.
USB hubs with external power supplies may improve the situation as they should provide the power for the hard disk. They can be useful if you encounter problems related to power (when the external hard disk is connected directly to your computer), for example:
the hard disk starts slowly
the hard disk makes the noise of starting/stopping when connected
the hard disk is automatically disconnected from the system during intensive disk operations
The above may happen if the computer can't provide enough power, even on double Y USB cable. This can happen with older systems or notebooks (especially when they working on batteries). In these situations, using an USB hub with an external power supply can help.
However, some USB hubs may cause compatibility or performance issues. Also the output of the small power supply is questionable, so it may be better to avoid using those USB hubs if possible when connecting hard disks. USB hubs are nice for less power-hungry devices of course.
The power supply of most USB hubs can provide up to 2000 mA (in theory, but in practice it may be less). This may be fine for a single USB hard disk and some devices like pendrives, Bluetooth adapter, etc. but not for two (or more) USB hard disks. So never attempt to connect two (or more) 2.5" external hard disks to such USB hubs because both the hard disks and the power supply of the USB hub can be damaged.
always use USB connections located on the rear panel of the motherboard when connecting external USB hard disks.
connect external hard disk drives to the computer / notebook with double Y USB cable.
always connect these 2 USB connections to the computer / notebook first and finally connect the one mini-USB end of the cable to the hard disk.
avoid using "front panel" USB connectors and USB extender cables when connecting external hard disks.
carefully use USB hubs, try one of them if required