Subject: Re: iSCSI:Text field in Asynchronous Message

From: "Tanjore K. Suresh" <[email-masked]>
Date: Thu, 14 Jun 2001 15:03:07 -0700 (PDT)

Kaladhar,

> Will there ever be a need for a Target to send an asynchronous Text message
> to the initiators (for potential performance optimizations)?

	So far in my opinion/understanding, the Initiator part is considered 
	to be the master and target responds to it to complete the 
	master's request. 
	
	But now you want the otherway in
	some conditions, i am wondering what those conditions are so that
	we can make a call.
	
> 
> According to the current iSCSI specification, the initiators can send Text
> messages to the target.
> Moreover, the initiators can send vendor specific X- key/values to the
> target.
> 
> Now, why can't the targets also have the ability to send X-key/value pairs
> to the initiators via Asynch messages?
> I would like input from people as to whether this feature will be useful.

	Assuming that you get this mechanism so that target can send the
	X-Key/value pair.
	
	If any action need to be taken on such X-Key/value pair that means
	Initiator should have known about the X-Key or such a vendor
	specific X-key should better be a well advertised one  between
	the initiator implementation and target implementation. 
	So, in my opinion, if the Intiator/Target knows about such a vendor
	unique X-Key, then why can't the Initiator implementation itself
	start negotiation for it with the assumption that  the target
	knows about it, if it not known anyway it could be rejected based 
	on the current specification definition of "none" and "reject" values.
	
	I am not able to get the point where it will be very much usefull.
	Please help me if am mistaken.
	
Thanks
sureshtk

---

From: Stephen Bailey <[email-masked]>
Date: Wed, 20 Jun 2001 11:57:01 -0400

> to the initiators

I can't speak to need, but it is allowed.

My reading of the intent of the spec (I'm not sure it says this as
well as it could, or even at all), is that targets can CERTAINLY
initiate X-* text message exchanges during full-feature mode.  The
semantics of an X-* message is entirely outside the spec, so sending
an X-* message may be a one-way operation (no response required), or a
multiway, handshaking deal, or whatever.

You could perform arbitrary vendor specific (or standardized
elsewhere) communication among targets and initiators using X-*
messages.  However, if your target wants to be a multitransport
creature (||SCSI, FCP & iSCSI), you're better off doing this
communication using some SCSI mechanism.  SCSI doesn't give you a
good, ubiquitous way for target-initiated messaging though, but there
are work-arounds.  What's often used is vendor specific sense on the
next command completion signal that the target wants to say something
to the initiator.

In other words, sure you can, and I suspect that initially many will
use this mechanism, but there are some strong reasons that it might
not take off as THE WAY to do out-of-band communcation.

Steph