Name that multi-port SCSI device

George Ericson gericson at mindspring.com
Mon Jun 7 20:55:23 PDT 1999


* From the T10 Reflector (t10 at symbios.com), posted by:
* "George Ericson" <gericson at mindspring.com>
*
Gene,

Your assertion that there is only one port per SCSI device is not supported
by the SAM or SAM-2 revisions prior to SAM2.9.  Here is some history from
the SAM and SAM-2 draft documents.  Please refer to the referenced drafts
for more detail.

The following text is excerpted from SAM rev13.

Definition of syntax for Instances from section 2.5.1.
---------------------------------------------------------------------------
{ } "instances of" A set of objects enclosed within curly brackets may occur
any number of times in a given instance. No physical ordering is implied.
The brackets may be indexed. For example, M{...}N indicates any number of
instances from M to N. Thus:
{...}3 implies 0, 1, 2 or 3 instances.
3{...} implies 3 or more instances. The upper limit is implementation or
protocol specific.
3{...}3 implies exactly 3 instances.
3{...}5 implies from 3 to 5 instances.

Definition of SCSI Device from SAM r13, April 1994
---------------------------------------------------------------------------
SCSI Device = [Initiator | Target | Target + Initiator]
Initiator = 0{Application Client} + 1{Initiator Identifier}
Target = 0{Logical Unit} + ( [Logical Unit 0 | Base Device]) + 1{Target
Identifier} + Task Manager
---------------------------------------------------------------------------
So this far back, we have the notion of one or more identifiers.
This is further clarified so that by the end of the SAM series we have.
Definition of SCSI Device from SAM r18, Nov 1995.
---------------------------------------------------------------------------
SCSI Device = [Initiator | Target | Target + Initiator] + 1{Service Delivery
Port}
Initiator = 0{Application Client}
Target = 0{Logical Unit} + Logical Unit 0 + 1{Target Identifier} + Task
Manager
---------------------------------------------------------------------------
So clearly SAM says that a SCSI Device can have one or more Service Delivery
Ports.

As late as SAM-2 r08, the SCSI Device is defined as:
---------------------------------------------------------------------------
An SCSI Device (see figure 12) is composed of one or more Service Delivery
Ports (see 4.6) combined with an Initiator, or a Target, or both an
Initiator and a Target.
---------------------------------------------------------------------------
The standard was changed in SAM-2 r09: in September 1998 which defines a
SCSI Device as:
---------------------------------------------------------------------------
In the basic structural model, an SCSI Device (see figure 12) is composed of
a Service Delivery Ports (see 4.6) combined with an Initiator, or a Target,
or both an Initiator and a Target.
---------------------------------------------------------------------------
You'll note that the plurality of Ports persists, even though the intent was
to change the definition to be only one Service Delivery Port.  This change
has been a point of contention ever since it was made.  As far as I know, no
public rational for this change has been made.  IMHO, the rational needs to
be fairly substantial to be acceptable since it removes functionality that
had been part of the standard since at least April 1994.  (i.e. for more
than 4 years previous.)  Additionally, there are many examples of commercial
multi-ported SCSI Devices that have been built to that standard.

George Ericson
CLARiiON Advanced Storage Division
Data General
GEricson at CLARiiON.com
(508) 480-7349



-----Original Message-----
From: owner-t10 at Symbios.COM [mailto:owner-t10 at Symbios.COM]On Behalf Of
Gene_Milligan at notes.seagate.com
Sent: Sunday, May 30, 1999 10:43 AM
To: Harlan Andrews
Cc: t10 at Symbios.COM
Subject: RE: Name that multi-port SCSI device


* From the T10 Reflector (t10 at symbios.com), posted by:
* Gene_Milligan at notes.seagate.com
*
<<I think the objection was to the SCSI part of the designation.>>

     The objection was a SCSI device used throughout the SCSI standards has
one target ID (in parallel one SCSI Bus ID), n LUNs, and one device server
per LUN. A multi-ported thingy has x target IDs, n LUNs (not xn LUNs, and
one device server per LUN. No objection to SCSI just to SCSI device unless
it conforms to the former.

Gene




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