Areca 24/4 Internal/External Port Pcie 3.0 12 Gb/s SAS/SATA Raid Controller 2Gb Cache - Manual (Page 29)

HARDWARE INSTALLATION
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Step 8. Install the LED Cable (Optional)
The preferred I/O connector for server backplanes is the Mini SAS
HD SFF-8643 connector. This connector has eight signal pins to
support four SAS/SATA drives and six pins for the SGPIO (Serial
General Purpose Input/Output) side-band signals. The SGPIO bus
is used for efficient LED management and sensing drive locate
status. See SFF 8485 for the specification of the SGPIO bus. For
backplane without enclosure SGPIO support, please refer to section
2.5 LED cables for fault/activity LED cable installation.
LED Management: The backplane may contain LEDs to indicate
drive status. Light from the LEDs could be transmitted to the out-
side of server by using light pipes mounted on the SAS drive tray.
A small microcontroller on the backplane, connected via the SGPIO
bus to a 12Gb/s SAS RAID controller, could control the LEDs. Activ-
ity: blinking 5 times/second and Fault: lit
Figure 2-10, Connect through HDD/CD Cable