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Re: Send Reject PDU when orignal to-be-rejected PDU is notavailable



David,
 
Oh, sorry I am wrong on that point, PDU headers don't have to be held until the status is sent and acked. I will make it correctly.
 
Thanks,
Jason




From: Black_David@xxxxxxx
Subject: RE: Send Reject PDU when orignal to-be-rejected PDU is notavailable
Date: Wed, 16 Apr 2008 10:24:49 -0400
To: hzj_wuying@xxxxxxxxxxx; ips@xxxxxxxx

But that only requires holding a Data-Out PDU header while the
corresponding data is in the RX pipe - once the data digest CRC
has been checked, the Data-Out PDU headers can be discarded -
they don't have to be held until the status is sent and acked.
 
Reject is primarily intended for errors that can be detected
on receipt of the PDU.
 
Thanks,
--David


From: HUJason [mailto:hzj_wuying@xxxxxxxxxxx]
Sent: Wednesday, April 16, 2008 2:13 AM
To: Black, David; ips@xxxxxxxx
Subject: RE: Send Reject PDU when orignal to-be-rejected PDU is notavailable

David,
 
In some situations, for example, one or more DATA-OUT PDUs of a WRITE are CRC ERROR. If the implementation(just like mine) choose to use Pipeline fashion process in which TX and RX are seperated as two stages, then it seems we have no choice but to hold those CRC ERROR DATA-OUT PDU headers until the REJECTs sent out. 
 
As we do not know how many DATA-OUT PDU will become CRC ERROR in RX stage, so we choose to reserve all DATA-OUT PDU headers in the end.


Best Regards,
Jason HU


From: Black_David@xxxxxxx
Subject: RE: Send Reject PDU when orignal to-be-rejected PDU is notavailable
Date: Wed, 16 Apr 2008 00:30:10 -0400
To: hzj_wuying@xxxxxxxxxxx; ips@xxxxxxxx

Jason,
 
The CmdSN window allows the target to control the resources consumed
by commands.  I don't understand the need to save "all PDU header
comes from the Initiator until corresponding statSN is explicitly
ACKed".  What purpose is that accomplishing (e.g., why save all
the iSCSI Data-Out PDU headers for a SCSI WRITE)?
 
In any case, the original PDU header is required for a Reject in order
for the initiator to figure out what was rejected.  If the initiator
cannot figure that out, it is going to have a very difficult time
recovering from the Reject.
 
Thanks,
--David
----------------------------------------------------
David L. Black, Distinguished Engineer
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953             FAX: +1 (508) 293-7786
black_david@xxxxxxx        Mobile: +1 (978) 394-7754
----------------------------------------------------


From: ips-bounces@xxxxxxxx [mailto:ips-bounces@xxxxxxxx] On Behalf Of HUJason
Sent: Tuesday, April 15, 2008 11:46 PM
To: Black, David; ips@xxxxxxxx
Subject: Re: Send Reject PDU when orignal to-be-rejected PDU is notavailable
 

Hi David,

Thank you for the suggestion. A little more to consider is that it seems that whatever mechanisms we use, as a target, we must reserve all PDU header comes from Initiator until the coressponding statSN is explicitly acked. For a resource-limted iscsi target engine(all SCSI data is on host, so it is not in this question), It can be considered as a big memory consumer and becomes a bottlenack.


Best Regards,
Jason

From: Black_David@xxxxxxx
Subject: RE: Send Reject PDU when orignal to-be-rejected PDU is notavailable
Date: Tue, 15 Apr 2008 23:04:15 -0400
To: hzj_wuying@xxxxxxxxxxx; ips@xxxxxxxx

The original PDU header has to be sent back so that the initiator
knows what was rejected.  iSCSI has a number of mechanisms that
can be used by the target to control resource consumption and
those should be used to ensure that adequate resources are
available to deal with the PDU that is to be rejected.
 
Thanks,
--David
----------------------------------------------------
David L. Black, Distinguished Engineer
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953             FAX: +1 (508) 293-7786
black_david@xxxxxxx        Mobile: +1 (978) 394-7754
----------------------------------------------------


From: ips-bounces@xxxxxxxx [mailto:ips-bounces@xxxxxxxx] On Behalf Of HUJason
Sent: Tuesday, April 15, 2008 9:59 PM
To: ips@xxxxxxxx
Subject: Send Reject PDU when orignal to-be-rejected PDU is notavailable

Dears,
I am curently implement iscsi target on a resource-limted device. In my implementation, orignal to-be-rejected PDU is not available when it realised that a Reject should be sent to initiator.
 
But as RFC3720 said, Target must send back the orignal PDU as the Reject's payload.
 
So my question is: Why we need to send back the orignal PDU ? Can we simply eliminate it?
 
Thanks!

Best Regards,

Jason 



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