The Oracle Server X5-2L is USB 2.0 compliant and meets all requirements from the USB 2.0 specification on both the front and back panel USB ports. Most external USB powered HDDs do not meet the USB 2.0 specification power draw of 500mA or less. The front and back USB ports have different layouts on the server, and there are electrical differences that make the front ports more sensitive to non-specification loads above 500mA.
When you plug any external USB powered hard disk drive (HDD), drawing more than the USB 2.0 specified 500mA, into the front USB ports, the host powers off due to an OverCurrent fault condition.
To prevent the host from powering off, install a flash drive, solid state drive (SSD), or hard disk drive (HDD) with an AC-powered USB enclosure in any USB port. Alternatively, use an inline bus powered hub in between the external USB powered device and the front port, for additional capacitance and to reduce the current spike recognized by the host, which allows you to also use the device on front USB ports.