Availability of Enclosure Services Interface implementation

snively at scsi snively at scsi
Thu Sep 28 09:19:16 PDT 1995

The Enclosure services interface implementation proposal has been
forwarded in post-script format to the SCSI ftp site.  I expect that it
will be placed in the publicly addressable directories some time this week.

For reference, I am including here some extracts of the text that describe
the proposal.



Using SCSI-3 technologies, disk drives and other SCSI devices may 
reside in subsystem enclosures some distance from the host initiators. 
To maintain a single communication interface with the host computer, 
it is important that any status information in the subsystem enclosure 
be available through the same SCSI interface that provides communications 
with the SCSI devices inside the enclosure. In addition, indicators, locks, 
and displays on the subsystem must be managed by the host through the 
SCSI interface. Very simple enclosures may make this information available 
through special ports to the standard SCSI devices. An example of such a 
port is the Enclosure Service Interface defined for SCA-2 attached 
devices by the Small Form Factor documents SFF-8045, SFF-8047, and SFF-8048. 
More sophisticated enclosures may actually create a special logical unit 
with its own or a shared target id that provides only enclosure services. 
While the method of accessing and setting such data is specified by this 
proposal, the actual data is mostly vendor unique, since the configuration 
and capabilities of each enclosure is unique. Some standard summary bits 
are defined for the convenience of monitoring software.

The SCSI-3 Controller Commands (SCC) document defines a MAINTENANCE IN 
and a MAINTENANCE OUT command. This command is not used for enclosure 
services because it is particular to the SCC model.

Enclosure Services capabilities:

Enclosure services can be implemented as a component of a standard 
SCSI device or as a separate LUN. The enclosure services commands 
are optional for any SCSI device. The proper place for this device 
model and the accompanying commands to be defined is SPC or a 
follow-on document to SPC. The commands used to transmit enclosure 
service information to or from the device are SEND DIAGNOSTIC and 
RECEIVE DIAGNOSTIC. A new diagnostic page is defined to contain the 
transmitted and received information. A page code is provided in 
RECEIVE DIAGNOSTIC to allow the explicit requesting of the desired 
enclosure status.

A set of functionality is made available to SCSI devices from the 
enclosure. One of these functions is the Enclosure Failure Warning, 
which may be generated by an enclosure to indicate to a SCSI device 
that a failure condition, including loss of primary power or cooling, 
has occurred. The action that the drive shall take upon detecting EFW, 
together with certain other enclosure related states, is set by a new 

The enclosure services device model defines a very simple device 
that is capable of being identified and tested as well as performing 
the transmission of enclosure services information. The processor 
device model and the communications device model are not appropriate 
because they mandate commands that cannot be implemented by the 
enclosure services device model.

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