Interpretation of Logical unit Reset behavior

Elliott, Robert (Server Storage) Elliott at
Fri Oct 18 16:08:22 PDT 2002

* From the T10 Reflector (t10 at, posted by:
* "Elliott, Robert (Server Storage)" <Elliott at>
This question was raised in March 2001 during the negotiation rewrite,
	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

Rob Elliott, elliott at
Industry Standard Server Storage Advanced Technology

> -----Original Message-----
> From: gerry.houlder at [mailto:gerry.houlder at] 
> Sent: Friday, October 18, 2002 4:26 PM
> To: t10 at
> Subject: Interpretation of Logical unit Reset behavior
> * From the T10 Reflector (t10 at, posted by:
> * gerry.houlder at
> *
> 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:
>    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 
>    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 or ACA (see 
> 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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