I_T Nexus reset TMF clarification

Ralph Weber roweber at ieee.org
Fri Mar 22 06:29:41 PDT 2013


* From the T10 Reflector (t10 at t10.org), posted by:
* Ralph Weber <roweber at ieee.org>
*
My recollection is that the I_T Nexus Loss task management function is 
also intended to assist bridge controller devices (e.g., a bridge device 
server that detects an I_T Nexus Loss with its application client can 
forward this to the SCSI target device by sending an I_T Nexus Loss task 
management function while acting in its (the bridge's) application 
client role).
In a similar vein, the fact that a Fibre Channel LOGO is the equivalent 
of an I_T Nexus Loss provides an additional interesting justification 
for the I_T Nexus Loss task management function.
All the best,
.Ralph
On 3/21/2013 11:21 AM, Gerry Houlder wrote:
> The original intent is that the I_T Nexus Loss TMF causes a SCSI 
> target to act in the same manner as if t has detected an I_T nexus 
> loss event on its own. This provides a way for a host to test the 
> behavior of a target and verify that the target performs all of the 
> requirements of an I_T nexus loss event. It is not useful in the case 
> of an actual I_T nexus loss event, as your email has surmised.
>
> An initiator might want to use this function to force a link reset/ 
> speed negotiation sequence without having to interact with an SMP device.
>
> On Thu, Mar 21, 2013 at 10:47 AM, Hannes Reinecke <hare at suse.de 
> > wrote:
>
>     * From the T10 Reflector (t10 at t10.org <mailto:t10 at t10.org>),
>     posted by:
>     * Hannes Reinecke <hare at suse.de >
>     *
>     Hi all,
>
>     SAM-5 states in section 7.6 (I_T Nexus reset):
>     >
>     > Each logical unit accessible through the SCSI target port shall
>     > perform the I_T nexus loss functions specified in
>     > 6.3.4 for the I_T nexus on which the function request
>     > was received, then:
>     >
>
>     Typically, when an I_T Nexus loss occurs the initiator can not
>     reach the target anymore. Depending on the transport, neither
>     side might be able to detect this condition automatically.
>
>     Hence the target might not be able to receive the TMF, nor
>     send a command completion.
>
>     So how is I_T nexus reset TMF supposed to be implemented?
>     As an ex-post TMF to be send after the I_T nexus has been
>     re-established?
>
>     Thanks for the clarification.
>
>     Cheers,
>
>     Hannes
>     -- 
>     Dr. Hannes Reinecke		    zSeries & Storage
>     hare at suse.de     +49 911 74053 688
>     SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
>     GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
>
>
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