SGPIO

Serial General Purpose Input/Output (SGPIO) is a four-signal (or four-wire) bus used between a host bus adapter (HBA) and a backplane. Of the four signals, three are driven by the HBA and one by the backplane. Typically, the HBA is a storage controller located inside a server, desktop, rack or workstation computer that interfaces with hard disk drives (HDDs) to store and retrieve data. It is considered an extension of the general-purpose input/output (GPIO) concept.

The SGPIO specification is maintained by the Small Form Factor committee in the SFF-8485 standard. The International Blinking Pattern Interpretation indicates how SGPIO signals are interpreted into blinking light-emitting diodes (LEDs) on disk arrays and storage backplanes.

The SGPIO signal consists of 4 electrical signals; it typically originates from a host bus adapter (HBA). iPass connectors carry both SAS/SATA electrical connections between the HBA and the hard drives as well as the 4 SGPIO signals.

A backplane is a circuit board with connectors and power circuitry into which hard drives are attached; they can have multiple slots, each of which can be populated with a hard drive. Typically the backplane is equipped with LEDs which by their colour and activity, indicate the slot's status; typically, a slot's LED will emit a particular colour or blink pattern to indicate its current status.

Although many hardware vendors define their own proprietary LED blinking pattern, the common standard for SGPIO interpretation and LED blinking pattern can be found in the IBPI specification.

On backplanes, vendors use typically 2 or 3 LEDs per slot - in both implementations a green LED indicates presence and/or activity - for backplanes with 2 LEDs per slot, the second LED indicates Status whereas in backplanes with 3 LEDs the second and third indicate Locate and Fail.

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