SCSI Enclosure Services (SES) is a protocol for more modern
SCSI
Small Computer System Interface (SCSI, ) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical and logical interface ...
enclosure
Enclosure or Inclosure is a term, used in English landownership, that refers to the appropriation of "waste" or " common land" enclosing it and by doing so depriving commoners of their rights of access and privilege. Agreements to enclose land ...
products. An
initiator can communicate with the enclosure using a specialized set of
SCSI command
In SCSI computer storage, computers and storage devices use a client-server model of communication. The computer is a client which requests the storage device to perform a service, e.g., to read or write data. The SCSI command architecture was ...
s to access power, cooling, and other non-data characteristics.
SES devices
There are two major classes of SES devices:
*
Attached enclosure services devices allow SES communication through a logical unit within one SCSI disk drive located in the enclosure. The disk-drive then communicates with the enclosure by some other method, the only commonly used one being
Enclosure Services Interface (ESI). In fault-tolerant enclosures, more than one disk-drive slot has ESI enabled to allow SES communications to continue even after the failure of any of the disk-drives. The definition of the ESI protocols is owned by an
ANSI
The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organ ...
committee and defined in their specifications ANSI SFF-8067 and SFF-8045.
*
Standalone enclosure services enclosures have a separate SES processor which occupies its own address on the SCSI bus. The protocol for this uses direct SCSI commands. An enclosure can be fault-tolerant by containing two SES processors.
SES commands
The SCSI initiator communicates with an SES device using two SCSI commands:
Send Diagnostic and
Receive Diagnostic Results. Some universal SCSI commands such as
Inquiry
An inquiry (also spelled as enquiry in British English) is any process that has the aim of augmenting knowledge, resolving doubt, or solving a problem. A theory of inquiry is an account of the various types of inquiry and a treatment of the ...
are also used with standalone enclosure services to perform basic functions such as initial discovery of the devices.
SES elements
The SCSI Send Diagnostic and Receive Diagnostic Results commands can be addressed to a specific SES element in the enclosure. There are many different
element codes defined to cover a wide range of devices. 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 be each given an 8-bit address.
When an SES controller is interrogated for the status of an SES element, the response includes a 4-bit
element status code. The most common element status codes are: 1h=OK, 2h=critical, 3h=warning, 5h=not installed.
SES element thresholds
Some SES elements, such as voltage sensors, current sensors, and temperature sensors, have a thresholding function. This allows an enclosure to detect and report unacceptable environmental conditions. The SCSI standard allows for two different threshold levels, noncritical (warning) and critical. Also, each threshold has a minimum and maximum value. So for example the threshold values for the 12 volt power-supply could be set as follows:
*Minimum critical - 10.8 volts
*Minimum noncritical - 11.4 volts
*Maximum noncritical - 12.6 volts
*Maximum critical - 13.2 volts
Threshold values are set by a Send Diagnostic command to the Threshold Out
diagnostic page (05h). Threshold values can be interrogated by a Receive Diagnostic Results command to the Threshold In diagnostic page (05h) with the PCV bit set to one.
Subenclosures
A larger SCSI storage enclosure may contain multiple subenclosures. The subenclosure with address 00h is designated the primary subenclosure and can return information about the other subenclosures.
SCSI attached enclosure services
SCSI attached enclosure services is a computer protocol used mainly with disk storage enclosures. It allows a host computer to communicate with the enclosure to access its power, cooling, and other non-data characteristics.
The host computer communicates with the disks in the enclosure via a SCSI interface which may be
Parallel SCSI
Parallel SCSI (formally, SCSI Parallel Interface, or SPI) is the earliest of the interface implementations in the SCSI family. SPI is a parallel bus; there is one set of electrical connections stretching from one end of the SCSI bus to the oth ...
,
FC-AL
The arbitrated loop, also known as FC-AL, is a Fibre Channel topology in which devices are connected in a one-way loop fashion in a ring topology. Historically it was a lower-cost alternative to a fabric topology. It allowed connection of ma ...
,
SAS, or
SSA. One of the disk devices located in the enclosure is set up to allow SCSI Enclosure Services (SES) communication through a logical unit. The disk-drive then communicates with the SES processor in the enclosure, usually via
Enclosure Services Interface (ESI), or a protocol called DSI for SSA enclosures. The data sent over the ESI or DSI interface is simply the contents of a
SCSI command
In SCSI computer storage, computers and storage devices use a client-server model of communication. The computer is a client which requests the storage device to perform a service, e.g., to read or write data. The SCSI command architecture was ...
and the response to that command.
Implemented commands
Only two SCSI commands are implemented by attached enclosure services devices:
See also
*
SES-2 Enclosure Management
*
SAF-TE — SCSI Attached Fault-Tolerant Enclosure
*
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 con ...
- Serial General Purpose Input/Output
* {{section link, bioctl#SES
*
hw.sensors
The hw.sensors framework is a kernel-level hardware sensors framework originating from OpenBSD, which uses the sysctl kernel interface as the transport layer between the kernel and the userland. , the framework is used by over a hundred devic ...
Computer data storage
Computer hardware tuning
Computer hardware standards
Computer performance
Motherboard
SCSI
System administration
System monitors