É mais seguro usar os dois, já que o Disco Rígido pode consumir mais Power on spin up, como o USB foi projetado.
Fourthly, many consumers and computer users buy 2.5” hard disk drives as portable storage devices inside USB chassis. A lot of chassis like that have no additional power supply, while a single USB connector can provide maximum 500mA current. So, some hard drives requiring a lot of power may face serious stability problems or may not be recognized by the system at all.
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