SCSI Enclosure Services
Encyclopedia
Most recent SCSI
enclosure
products support a protocol called SCSI Enclosure Services (SES). The initiator
can communicate with the enclosure using a specialised set of SCSI command
s to access power, cooling, and other non-data characteristics.
and Receive Diagnostic Results
. Some universal SCSI commands such as Inquiry
are also used with standalone enclosure services to perform basic functions such as initial discovery of the devices.
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 a SES controller is interrogated for the status of a 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.
ISA
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.
The host computer communicates with the disks in the enclosure via a SCSI interface which may be Parallel SCSI
, FC-AL
, 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
and the response to that command.
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
enclosure
Disk enclosure
A disk enclosure is essentially a specialized chassis designed to hold and power disk drives while providing a mechanism to allow them to communicate to one or more separate computers. Drive enclosures provide power to the drives therein and convert the data sent across their native data bus into a...
products support a protocol called SCSI Enclosure Services (SES). The initiator
SCSI initiator
In computer data storage, a SCSI initiator is the endpoint that initiates a SCSI session, that is, sends a SCSI command. The initiator usually does not provide any Logical Unit Numbers ....
can communicate with the enclosure using a specialised set of SCSI command
SCSI command
In SCSI computer storage, a command is the basic unit of communication. The SCSI command architecture was originally defined for parallel SCSI buses but has been carried forward with minimal change for use with Fibre Channel, iSCSI and Serial Attached SCSI....
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 InterfaceEnclosure Services InterfaceThe Enclosure Services Interface is a computer protocol used in SCSI enclosures. This is part of a chain of connections that allows a host computer to communicate with the enclosure to access its power, cooling, and other non-data characteristics...
(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 ANSIAnsiAnsi is a village in Kaarma Parish, Saare County, on the island of Saaremaa, Estonia....
committee and defined in their specifications ANSI SFF-8067 and SFF-8045.
- Standalone enclosure servicesSCSI standalone enclosure servicesSCSI standalone 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....
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 DiagnosticSCSI Send Diagnostic Command
The SCSI Send Diagnostic command is used to instruct a target device to perform a self-test on a specific LUN. The CDB structure is:The special parameter fields in the CDB have the following meaning:*PF - Page Format:...
and Receive Diagnostic Results
SCSI Receive Diagnostic Results Command
The SCSI Receive Diagnostic Results command is used to interrogate the results of a self-test. The self-test must have been triggered by a previous Send Diagnostic command which would have defined the self-test required. This is usually associated with one of the available diagnostic pages.The...
. Some universal SCSI commands such as Inquiry
SCSI Inquiry Command
The SCSI Inquiry command is used to obtain basic information from a target device. The CDB structure is:If the EVPD parameter bit is zero and the Page Code parameter byte is zero then the target will return the standard inquiry data, which is structured as follows:The special fields in 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 codesSCSI element codes
SCSI Enclosure Services 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.-List of SES element codes:...
defined to cover a wide range of devices. The most common SES elements are power supply, cooling fan, temperature sensor, and UPS
Uninterruptible power supply
An uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power, fails...
. 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 a SES controller is interrogated for the status of a SES element, the response includes a 4-bit element status code
SCSI element status codes
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 element...
. The most common element status codes are: 1h=OK, 2h=critical, 3h=warning, 5h=not installed.
ISA
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
SCSI diagnostic pages
SCSI target devices provide a number of SCSI diagnostic pages. These can be used by a Send Diagnostic command to tell a target device to run a specialised self-test. The Receive Diagnostic Results command is used where the results from the self-test operation are non-trivial.Most of the common...
(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
Parallel SCSI is one of the interface implementations in the SCSI family. In addition to being a data bus, SPI is a parallel electrical bus: There is one set of electrical connections stretching from one end of the SCSI bus to the other. A SCSI device attaches to the bus but does not interrupt it...
, FC-AL
Arbitrated loop
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 many servers and computer storage devices without using then...
, SAS
Serial Attached SCSI
Serial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,...
, or SSA
Serial Storage Architecture
Serial Storage Architecture is a serial transport protocol used to attach disk drives to servers. It was invented by Ian Judd of IBM in 1990...
. 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)
Enclosure Services Interface
The Enclosure Services Interface is a computer protocol used in SCSI enclosures. This is part of a chain of connections that allows a host computer to communicate with the enclosure to access its power, cooling, and other non-data characteristics...
, 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
SCSI command
In SCSI computer storage, a command is the basic unit of communication. The SCSI command architecture was originally defined for parallel SCSI buses but has been carried forward with minimal change for use with Fibre Channel, iSCSI and Serial Attached SCSI....
and the response to that command.
Implemented commands
Only two SCSI commands are implemented by attached enclosure services devices:| SCSI command | Operation code | Comment |
|---|---|---|
| RECEIVE DIAGNOSTIC RESULTS SCSI Receive Diagnostic Results Command The SCSI Receive Diagnostic Results command is used to interrogate the results of a self-test. The self-test must have been triggered by a previous Send Diagnostic command which would have defined the self-test required. This is usually associated with one of the available diagnostic pages.The... |
1Ch | Mandatory |
| SEND DIAGNOSTIC SCSI Send Diagnostic Command The SCSI Send Diagnostic command is used to instruct a target device to perform a self-test on a specific LUN. The CDB structure is:The special parameter fields in the CDB have the following meaning:*PF - Page Format:... |
1Dh | Mandatory |
See also
- SCSI Attached Fault-Tolerant EnclosureSAF-TEIn computer storage, a SCSI Accessed Fault-Tolerant Enclosure is an industry standard to interface an enclosure to a SCSI subystem to gain access to information or control concerning* temperature* fan status* slot status...
- SGPIOSGPIOSGPIO is an acronym for Serial General Purpose Input/Output which is a 4-signal bus used between a host bus adapter and a backplane; of the 4 signals, 3 are driven by the HBA and 1 by the backplane...
- Serial General Purpose Input/Output