Enclosure Services Interface
Encyclopedia
The Enclosure Services Interface (ESI) 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. This overall approach is called SCSI attached enclosure services:
The host computer communicates with the disks in the enclosure via a Serial SCSI interface (which may be either FC-AL
or SAS
). One of the disk devices located in the enclosure is set up to allow SCSI Enclosure Services
(SES) communication through a LUN. The disk-drive then communicates with the SES processor in the enclosure via ESI. The data sent over the ESI interface is simply the contents of a SCSI command
and the response to that command.
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.
) of a disk-drive. An extra eighth signal called "-PARALLEL ESI" is used to switch the function of the SEL_n signals.
or Receive Diagnostic Results command is sent from the host computer to the disk-drive to initiate an SES transfer. The Disk-drive then asserts "-PARALLEL ESI" to begin this sequence of ESI bus phases:
Finally, the disk-drive deasserts "-PARALLEL ESI".
The above sequence is just a simple implementation of a 4-bit wide parallel interface which is used to execute a SCSI transaction. If the CDB is for a Send Diagnostic command then the data is sent to a SCSI diagnostic page
in the enclosure. If the CDB is for a SCSI Receive Diagnostic Results command then the data is received from a SCSI diagnostic page. No other CDB types are allowed.
committee and defined in their specifications ANSI SFF-8067 and ANSI SFF-8045.
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...
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. This overall approach is called SCSI attached enclosure services:
The host computer communicates with the disks in the enclosure via a Serial SCSI interface (which may be either 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...
or 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,...
). One of the disk devices located in the enclosure is set up to allow SCSI Enclosure Services
SCSI Enclosure Services
Most recent SCSI enclosure products support a protocol called SCSI Enclosure Services . The initiator can communicate with the enclosure using a specialised set of SCSI commands to access power, cooling, and other non-data characteristics.-SES devices:...
(SES) communication through a LUN. The disk-drive then communicates with the SES processor in the enclosure via ESI. The data sent over the ESI 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.
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.
ESI electrical interface
The ESI interface was designed to make use of the seven existing "SEL_n" address signals which are used at power-on time for establishing the address (ALPAFibre Channel network protocols
Communication between devices in a fibre channel network uses different elements of the Fibre Channel standards. The following sections introduce the main concepts and show how a combination of primitives and frames is required....
) of a disk-drive. An extra eighth signal called "-PARALLEL ESI" is used to switch the function of the SEL_n signals.
| Signal name | Function |
| The disk-drive asserts this signal to use the SEL_n signals for ESI | |
| SEL_0/D0 | Data bus bit 0 |
| SEL_1/D1 | Data bus bit 1 |
| SEL_2/D2 | Data bus bit 2 |
| SEL_3/D3 | Data bus bit 3 |
| SEL_4/-ENCL_ACK | The enclosure clocks this to acknowledge a read or write data transfer |
| SEL_5/-DSK_RD | The disk-drive clocks this to send a NIBL of data to the enclosure |
| SEL_6/-DSK_WR | The disk-drive clocks this to receive a NIBL of data from the enclosure |
ESI command sequence
A SCSI Send Diagnostic commandSCSI 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:...
or Receive Diagnostic Results command is sent from the host computer to the disk-drive to initiate an SES transfer. The Disk-drive then asserts "-PARALLEL ESI" to begin this sequence of ESI bus phases:
| Phase | Function | |
| Discovery phase | Disk-drive tests that the enclosure is SFF-8067 compliant | |
| Command phase | Disk-drive sends the SCSI CDB to the enclosure (similar to the write phase) | |
| Either | Read phase | Disk-drive sends diagnostic page data to the enclosure |
| or | Write phase | Disk-drive receives diagnostic page data from the enclosure |
Finally, the disk-drive deasserts "-PARALLEL ESI".
The above sequence is just a simple implementation of a 4-bit wide parallel interface which is used to execute a SCSI transaction. If the CDB is for a Send Diagnostic command then the data is sent to a SCSI 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...
in the enclosure. If the CDB is for a SCSI Receive Diagnostic Results command then the data is received from a SCSI diagnostic page. No other CDB types are allowed.
Alternatives to ESI
There are two common alternatives ESI:- 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....
uses a direct connection which does not require ESI - SSASerial Storage ArchitectureSerial Storage Architecture is a serial transport protocol used to attach disk drives to servers. It was invented by Ian Judd of IBM in 1990...
enclosures use an interface called DSI which is similar to ESI
Specifications
The definition of the ESI protocols is owned by an ANSIAnsi
Ansi is a village in Kaarma Parish, Saare County, on the island of Saaremaa, Estonia....
committee and defined in their specifications ANSI SFF-8067 and ANSI SFF-8045.