Name that multi-port SCSI device

George M. Ericson GEricson at BAnet.net
Tue May 25 18:52:01 PDT 1999


* From the T10 Reflector (t10 at symbios.com), posted by:
* "George M. Ericson" <GEricson at BAnet.net>
*

Brian,

Some comments inline on your issues:  (Interesting list...)  The answer to
the first may surprise you.

George


Here are some issues:

1) How does an event on a port of a "thingy" affect the other ports?  Does
LU to port mapping modify the behavior?
For example:  A "thingy" has logical units X, Y, and Z. and ports A B and C.
LU X is connected to ports A and B.  LU Y is connected to Ports B and C.  LU
Z is only connected to port C.  If a target reset task management function
is received by Port A what happens to LUs attached to ports B and C?  What
does an initiator with a nexus to LU Z through Port C experience?
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GME: This is not an example of a multi-ported target.  Here is my reasoning.
In SAM-2.10, an LU is part of a SCSI Target, (4.7.2).  So, based on that,
this must be a composite device.  There are between three and six individual
targets.

I'll name target by Port as in Tab would be a multi-ported target addressed
by both ports A and B.  No multi-ported targets are in this example.  The
LUs are unqualified if they are lowest level.  Mappings through to LUs (as
in Virtual Devices)are tagged with the underlying port that they map to.
I'll tag with the same letter to indicate don't care.

Here are some of the possible combinations:
a) Ta(X), Tb(Xa,Yc), Tc(Y,Z)
b) Td(X,Y,Z) Ta(Xd), Tb(Xd,Yd), Tc(Yd,Zd)
c) Td(X), Te(Y), Tf(Z), Ta(Xd), Tb(Xd,Ye), Tc(Ye,Zf)
...

So, the question was about a TARGET RESET to Port A.  A TARGET RESET is a
Task Management function that is simply broadcast as LU RESETS to all LUs of
the target.  So, a TARGET RESET on A will propagate to Ta which will do an
LU RESET on LU Xx.  If Xx is a virtual device, then the LU RESET will get
propogated down until it reaches the bottom.  In this case, all initiators
attached to Ta and Tb will each experience a Unit Attention on their next
access to Xx.  Neither LUs Yy or Zz are affected by the LU RESET so Unit
Attentions are not propagated through them.
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2) If an initiator needs to identify the same LU regardless of service
deliver port, how is this done?
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GME: This is available for non-thingy's as INQUIRY Vital Product Data Device
Identification Page 83h.  Logical Unit Identifier with Identifier Type =
1,2, or 3.
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---

3) If a "thingy" needs to be able to identify the same initiator attached to
multiple "thingy" ports, how is this done?
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GME: This would be new functionality. What motivates the requirement?
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4) If a target "thingy" needs to identify an initiator "thingy" regardless
of initiator or target ports how is it done?
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GME: This would be new functionality. What motivates the requirement?
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---

5) Does a target "thingy" do something different for multiple nexuses from
the same initiator "thingy" versus nexuses from different initiators.  Is
anything different done if multiple initiator "thingy" ports are attached to
the same target port?
----------------------------------------------------------------------------
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GME: No, No.
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---

--

Brian McKean                             Voice: (303)381-4246
Mylex Corporation External Products      Fax:   (303)413-0464
4900 Pearl East Circle Suite 104         brianmylexboulder.com
Boulder, CO 80301-6108
http://www.mylex.com





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