Raid контроллер Adaptec ASR-2405

Это так называемый sideband кабель (SFF-8448)
Используется для подключения к дополнительным устройствам/индикаторам на панели сервера, которые смогут следить/отображать работу самого контроллера

The sideband cables are used to connect the controller to a managed backplane or disk enclosure, so that it can monitor the controller as well as the disks.

из мануала. .
SAS fan-out cables are also available with an additional sideband (SFF-8448) cable
that caries SGPIO signals for enclosure management. This additional sideband cable is not
used with direct-attached disk drives.

Из Wiki:
http://en.wikipedia.org/wiki/SGPIO
SGPIO is an acronym for Serial General Purpose Input/Output which is a 4-signal (or 4-wire) bus used between a host bus adapter (HBA) and a backplane; of the 4 signals, 3 are driven by the HBA and 1 by the backplane. Typically, the HBA is a storage controller located inside a server, desktop, rack or workstation computer which interfaces with hard disk drives (HDDs) to store and retrieve data.
The SGPIO specification has the official name SFF-8485 and is maintained by the SFF Committee. The International Blinking Pattern Interpretation which indicates how SGPIO signals are interpreted into blinking LEDs on disk arrays and storage backplanes is described in the article IBPI.

Мануал в ломы почитать?

для работы рейда он не нужен, 100% .. но какие функции на него возлагаются- не отвечу :)

Кури электронный мануал, если нет бумажного. Мне лень
http://www.adaptec.com/en-US/support/raid/sas_raid/SAS-2405/_docs/Adaptec_RAID_Controller_IUG_8_2010_pdf.htm?nc=/en-US/support/raid/sas_raid/SAS-2405/_docs/Adaptec_RAID_Controller_IUG_8_2010_pdf.htm