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 commands to access power, cooling, and other non-data characteristics. In Computer storage, a SCSI initiator is the endpoint that initiates a SCSI session that is sends a SCSI command In SCSI Computer storage, a command is the basic unit of communication
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SES devices
There are two major classes of SES devices:
- Attached enclosure services devices allow SES communication through a LUN within one SCSI disk-drive located in the enclosure. Most recent SCSI enclosure products support a protocol called SCSI Enclosure Services (SES The disk-drive then communicates with the enclosure by some other method, the only commonly used one being Enclosure Services Interface (ESI). The Enclosure Services Interface (ESI is a computer protocol used in SCSI enclosures 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 committee and defined in their specifications ANSI SFF-8067 and SFF-8045.
- Standalone enclosure services devices have a separate SES processor which occupies its own address on the SCSI bus. SCSI standalone enclosure services is a computer protocol used mainly with disk storage enclosures The protocol for this uses direct SCSI commands. Fault-tolerance can be achieved by having two SES processors in the same enclosure.
SES commands
The SCSI initiator communicates with an SES device using two SCSI commands: Send Diagnostic and Receive Diagnostic Results. The SCSI Send Diagnostic command is used to instruct a target device to perform a self-test on a specific LUN. The SCSI Receive Diagnostic Results command is used to interrogate the results of a self-test 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. The SCSI Inquiry command is used to obtain basic information from a target device
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. SCSI Enclosure Services (SES devices contains a number of elements each of which is defined by a one byte SCSI element code. The most common SES elements are power supply, cooling fan, temperature sensor, and UPS. An uninterruptible power supply ( UPS) also known as a continuous power supply ( CPS) or a battery backup is a device which maintains a continuous 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. 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 most common element status codes are: 1h=OK, 2h=critical, 3h=warning, 5h=not installed.
SES element thresholds
Some SES elements like voltage sensors, current sensors, and temperature sensors support thresholding. 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). SCSI target devices provide a number of SCSI diagnostic pages. 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, FC-AL, SAS, or SSA. Parallel SCSI (formally SCSI Parallel Interface, or SPI) is one of the interface implementations in the SCSI family 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 Introduction A typical Serial Attached SCSI system consists of the following basic components An Initiator is a device that originates device service Serial Storage Architecture (SSA is a serial transport protocol used to attach Disk drives to servers It was invented by Ian Judd of IBM in One of the disk devices located in the enclosure is set up to allow SCSI Enclosure Services (SES) communication through a LUN. In Computer storage, a logical unit number or LUN is simply the number assigned to 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 Enclosure Services Interface (ESI is a computer protocol used in SCSI enclosures The data sent over the ESI or DSI interface is simply the contents of a SCSI command and the response to that command. In SCSI Computer storage, a command is the basic unit of communication
Supported commands
Only two SCSI commands are supported by attached enclosure services devices:
| SCSI command | Operation code | Comment |
|---|---|---|
| RECEIVE DIAGNOSTIC RESULTS | 1Ch | Mandatory |
| SEND DIAGNOSTIC | 1Dh | Mandatory |
External links
The SCSI Receive Diagnostic Results command is used to interrogate the results of a self-test The SCSI Send Diagnostic command is used to instruct a target device to perform a self-test on a specific LUN.Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic