ESI meaning in Computing ?

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.