Interpretation of Logical unit Reset behavior

Binford, Charles CBinford at pirus.com
Mon Oct 21 16:10:38 PDT 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* "Binford, Charles" <CBinford at Pirus.com>
*
Robert,  while I agree with your conclusion, I think it is hard to justify your last statement, "TARGET RESET does the target port resetting." from any words I can find in SAM-2.  Everywhere I looked Target Reset was merely a LUN reset to each LU.  My reading says the result of a host sending a LUN Reset to each LU, and a host sending a Target Reset would be the same.  I don't see anything to suggest Target Reset should have special handling of the port parameters.  What did I miss?

Charles Binford
Pirus Networks
316.315.0382 x222


-----Original Message-----
From: Elliott, Robert (Server Storage) [mailto:Elliott at hp.com]
Sent: Friday, October 18, 2002 6:08 PM
To: t10 at t10.org
Subject: RE: Interpretation of Logical unit Reset behavior


* From the T10 Reflector (t10 at t10.org), posted by:
* "Elliott, Robert (Server Storage)" <Elliott at hp.com>
*
This question was raised in March 2001 during the negotiation rewrite,
and 
	01-128r2 (1 May 2001) SPI-4 reset cleanup 
added the rule that LOGICAL UNIT RESET shall not affect the negotiation.


Negotiated settings are a property of the target port shared by all the
logical units. In a target with multiple logical units, reset of one of
the logical units shouldn't affect the others' ability to communicate.

SAM-2 just says the logical unit should be returned to a power-on-like
state, not the target port.  TARGET RESET does the target port
resetting.

--
Rob Elliott, elliott at hp.com
Industry Standard Server Storage Advanced Technology
Hewlett-Packard



> -----Original Message-----
> From: gerry.houlder at seagate.com [mailto:gerry.houlder at seagate.com] 
> Sent: Friday, October 18, 2002 4:26 PM
> To: t10 at t10.org
> Subject: Interpretation of Logical unit Reset behavior
> 
> 
> * From the T10 Reflector (t10 at t10.org), posted by:
> * gerry.houlder at seagate.com
> *
> A contradiction has been pointed out for the description of 
> the Logical Unit Reset behavior. In particular, note the 
> requirements I have marked with double brackets << >>.
> 
> From SPI - 4 or 5:
> 
>    16.5.6 LOGICAL UNIT RESET
>    The LOGICAL UNIT RESET message is defined in the SCSI Architecture
>    Model-2 standard.
>    Receipt of the LOGICAL UNIT RESET message after an I_T_L 
> nexus has been
>    established is a logical
>    unit reset event as defined in the SCSI Architecture 
> Model-2 standard.
>    In addition to the requirements in the SCSI Architecture Model-2
>    standard the SCSI target port shall go to
>    the BUS FREE phase following the successful receipt of the 
> LOGICAL UNIT
>    RESET message.
> 
>    <<A logical unit reset has no effect on the transfer agreement.>>
> 
> From SCSI Architecture Model-2 standard
> 
>    5.9.7 Logical unit reset
>    A logical unit reset is:
>    a) The action in response to a LOGICAL UNIT RESET task management
>    request (see 6.6) or some other
>    logical unit reset event; or
>    b) One of the actions in response to a TARGET RESET task management
>    function (see 6.7) or a hard reset
>    (see 5.9.6).
>    The definition of logical unit reset events is dependent 
> on the SCSI
>    transport protocol.
>    To process a logical unit reset the logical unit shall:
>    a) Abort all tasks as described in 5.7;
>    b) Clear a CA (see 5.9.1.6) or ACA (see 5.9.1.7) 
> condition, if one is
>    present;
>    c) Release all reservations established using the reserve/release
>    management method (persistent reserva-tions
>    shall not be affected);
>    <<d) Return the logical unit's operating mode to the 
> appropriate initial
>    conditions, similar to those conditions that
>    would be found following device power-on.>> The MODE 
> SELECT parameters
>    (see SPC-2) shall be restored
>    to their last saved values if saved values have been 
> established. MODE
>    SELECT parameters for which no
>    saved values have been established shall be returned to 
> their default
>    values;
>    e) Set an unit attention condition (see 5.9.5); and
>    f) Initiate a logical unit reset for all dependent logical 
> units (see
>    4.13).
>    In addition to the above, the logical unit shall perform 
> any additional
>    functions required by the applicable standards.
> 
> The wording from SPI says "no effect on transfer agreement", 
> meaning the target has to remember the transfer agreement 
> even though everything else is being reset. The SAM wording 
> says "similar to power on", which certainly includes 
> resetting the transfer agreement. These conditions certainly 
> conflict with each other. How do we resolve the conflicting wording?
> 
> The single LUN targets I am familiar with reset all the same 
> things (including the transfer agreement) for both of these 
> functions. Are these devices in violation of the standard?
> 
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