Subject: RE: [Ips] Behavior of iSCSI initiator , in case of Data-Out PDU D igest Error ?

From: [email-masked]
Date: Mon, 23 Feb 2004 15:39:06 -0500

> Section 6.2.1 of Spec says that "Retry of Commands MUST NOT be used for
> reasons other than plugging command sequence gaps." So I believe that
> you no need to retry the command from iSCSI driver for this case. Is
> this correct folks?

That's correct.  Because status has been received (CHECK CONDITION),
the command has completed from both the initiator and target
perspective.  The driver is allowed to resubmit the command to
the target, but is not required to; the CHECK CONDITION can be
reported upward to SCSI if the driver chooses to do so.  If the
driver resubmits the command, that is a *new* command as far as
iSCSI is concerned, so it MUST use a new CmdSN, and it's a good
idea (although not required) to use a new Initiator Task Tag.

Be careful about repeated resubmissions of this form - there is
often higher level SCSI software (e.g., multipathing) that is
operating off of a timeout based on failure to receive a response
to a command; it would be bad for that software to go into motion
to try to get the command accomplished (e.g., via another path)
while the driver is trying to do the same thing.

Thanks,
--David
----------------------------------------------------
David L. Black, Senior Technologist
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953             FAX: +1 (508) 293-7786
[email-masked]        Mobile: +1 (978) 394-7754
----------------------------------------------------

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On 
> Behalf Of Ramesh Mangamuri
> Sent: Monday, February 23, 2004 12:58 PM
> To: [email-masked]; [email-masked]
> Subject: RE: [Ips] Behavior of iSCSI initiator , in case of 
> Data-Out PDU Digest Error ?
> 
> 
> Section 6.2.1 of Spec says that "Retry of Commands MUST NOT be used for
> reasons other than plugging command sequence gaps." So I believe that
> you no need to retry the command from iSCSI driver for this case. Is
> this correct folks?
> 
> -----Original Message-----
> From: Naveen Burmi [mailto:[email-masked]] 
> Sent: Monday, February 23, 2004 3:57 AM
> To: [email-masked]
> Subject: [Ips] Behavior of iSCSI initiator , in case of Data-Out PDU
> Digest Error ?
> 
> 
> Need some clarification on the behavior of iSCSI initiator under the 
> following condition:
> 
> One of the data PDUs received by the target fails to pass Data Digest
> Check. 
> The target (542x) rejects the Data PDU with reason code Data Digest
> Error. 
> The target eventually terminates the task with a response PDU with a
> CHECK 
> CONDITION Status and an iSCSI Condition of "protocol service 
> CRC error".
> 
> Are we allowed to retry the command within the iSCSI driver?
> If yes, does the CmdSN, itt need to be the same?
> 
> Thanks,
> Naveen.
> 
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