RE: LUN field in R2T

[Julian Satran <Julian_Satran@xxxxxxxxxx>]

Bill,

This is left to the implementer. I would
argue that a "liberal" initiator should store the LUN-TTT fields
as they come and not fill them up.

Julo


Sears_Bill@xxxxxxx wrote on 01/04/2008 02:36:03 AM:

> Thanks for getting back on this.   I think I still need a little
clarification.
>  
> In a nutshell all I want to know is this:  Is
it legal for an 
> initiator to set the LUN field in the Data-Out PDU based on what it
> knows the LUN to be, or MUST the initiator copy the contents of the
> LUN field from the received R2T into the Data Out. 
>  
> Example:  An initiator negotiates for MaxOutstandingR2T==4.
 The 
> initiator sends a write command to a target.  The initiator receives
> an R2T and starts sending multiple Data-Out PDUs.   The initiator
> receives 3 more R2Ts but cannot start sending Data-Out PDUs 
> immediately due to outbound resource limitations.   The initiator
must
> now store off each R2T request so that it can honor them when 
> resources become available – otherwise the initiator will need to
halt
> receive processing on the connection.   The initiator will probably
> need to store the Target Transfer Tag, Buffer Offset, and Desired
Data
> Transfer Length for each R2T.   Does the initiator need to store
the 
> LUN from each R2T as well?  Or can it just fill in the LUN in
the Data
> Out PDUs based on knowing what LUN the command was sent to in the
first place? 
>  
> Thanks,
>  
>  
> Bill
>  
>  
>  
> 
> From: Julian Satran [mailto:Julian_Satran@xxxxxxxxxx] 
> Sent: Thursday, January 03, 2008 4:12 AM
> To: Sears, Bill
> Cc: ips@xxxxxxxx
> Subject: Re:  LUN field in R2T
>  
> 
> Your interpretation is more liberal than the text says. The reason
for
> requiring a LUN field in the first place was to remove the requirement
> for a  target-wide unique TTT and enable distributed targets
that do 
> not require coordination.  The reason LUN was chosen to tag the
R2T is
> that it may simplify routing of the data to the appropriate destination.
> But since it is called LUN some zealous initiator may check (although
> it is not mandated) the LUN validity versus a list obtained otherwise
> - so I would not go for a very liberal interpretation. 
> 
> Julo 

> 
> Sears_Bill@xxxxxxx 
> 01/02/08 11:57 PM 
> 
> To
> 
> <ips@xxxxxxxx> 
> 
> cc
> 
>  
> 
> Subject
> 
>  LUN field in R2T
> 
>  
> 
>  
> 
>  
> 
> 
> 
> 
> Just a quick clarification: 
>   
> 10.8.5.  Target Transfer Tag 
> [...]The Target Transfer Tag and LUN are copied in the outgoing data
> PDUs and are only used by the target. 
>   
> Does this mean that the LUN field in the R2T does not need to contain
> the actual LUN number specified by the SCSI write?   Since the
field 
> is “only used by the target” I assume this text means that the target
> may place anything it wants in the LUN field of the R2T and have it
> echoed back by the initiator. 
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