SCSI Enclosure Services (SES) devices contains a number of elements, each of which is defined by a one byte SCSI element code. There are many different element codes defined to cover various devices as shown in the list below.
00h - unspecified01h - device - disk-drive or other SCSI device02h - power-supply03h - cooling04h - temperature-sensor05h - door lock06h - audible alarm07h - enclosure services controller electronics08h - SCC controller electronics09h - nonvolatile cache0Ah - invalid operation reason - used to determine why an ESI device has failed to complete a command0Bh - UPS0Ch - display0Dh - keypad0Eh - enclosure0Fh - SCSI port/transceiver10h - language11h - communication port12h - voltage sensor13h - current sensor14h - SCSI target port15h - SCSI initiator port16h - simple subenclosure17h - array device18h - SAS expander19h - SAS connector1Ah-7Fh - reserved80h-FFh - vendor-specificThe SCSI initiator communicates with an SES device using two SCSI commands, Send Diagnostic and Receive Diagnostic Results. The most common SES elements are power-supply, cooling-fan, temperature-sensor and UPS. The SCSI command protocols assume that there may be more than one of each device type so they must each be given an 8-bit address. When the SES controller is interrogated for the status of an SES element, the response includes a 4-bit status code. The most common element status codes are: 1h=OK, 2h=critical, 3h=warning, 5h=not installed.
See the SES article for a more detailed description.
When a SCSI SES controller is interrogated for the status of a SES element, the response includes a 4-bit SCSI element status code. The list of valid codes is:
0h - unsupported - status detection is not implemented for this element1h - OK - element is installed and no error conditions are known2h - critical - critical condition is detected3h - noncritical (warning) - noncritical condition is detected4h - unrecoverable - unrecoverable condition is detected5h - not installed - this element is not installed in the enclosure6h - unknown - sensor has failed or element status is not available7h - not available - element installed, no known errors, but the element has not been set into operation8h-Fh - reserved 