Subject: iSCSI RE: Phase collapse

From: [email-masked]
Date: Fri, 9 Nov 2001 18:55:37 -0500

Yes, most of the time:
- If the INQ succeeds, a single Data-in PDU can carry the
    successful status without a Response PDU.
- If the INQ fails without transferring any data, a single
    Response PDU carries the status and autosense info.
    Recall that autosense is REQUIRED by iSCSI.
But
- If the INQ transfers data and then fails, a Data-In PDU
    is needed to transfer the data and a Response PDU is
    needed to transfer the status and autosense info.
 
--David
 
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David L. Black, Senior Technologist
EMC Corporation, 42 South St., Hopkinton, MA  01748
+1 (508) 435-1000 x75140     FAX: +1 (508) 497-8500
[email-masked]       Mobile: +1 (978) 394-7754
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-----Original Message-----
From: Ken Nicholson [mailto:[email-masked]]
Sent: Wednesday, October 31, 2001 9:45 AM
To: [email-masked]'
Subject: Phase collapse

Julian and David: 

Could you clarify the information below? 

It seems to us that it should be possible for a target to phase collapse the
response to an INQ in a single PDU which is both the first and last PDU of
that response.

If this true: 
>A command and its associated data may be 
> shipped together from initiator to target and data and responses 
> may be shipped together from targets." 

Why is this true: 
"...the above text makes 
it quite clear that data transferred by the action of a SCSI command 
(including Read, Inquiry, Mode Sense, and Read Capacity) cannot be put in 
the Response PDU. " 

Ken Nicholson 
iReady Corp. 

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To: [email-masked] 
Subject: RE: iSCSI: Inquiry, Mode Sense, Read Capacity 
From: "Julian Satran" <[email-masked]> 
Date: Wed, 3 Oct 2001 22:46:44 +0300 
Content-Type: multipart/alternative; boundary="=_alternative 
006CB109C2256ADA_=" 
Sender: [email-masked] 

David is right. Response doe not contain data proper. 
Phase collapse is for the last DataPDU in which a target can fit a GOOD 
status (and thus avoid an additional response) and some residual counts 
(when those are not considered errors). 

Julo 

[email-masked] 
Sent by: [email-masked] 
03-10-01 20:21 
Please respond to Black_David 

        To:        [email-masked], [email-masked] 
        cc: 
        Subject:        RE: iSCSI: Inquiry, Mode Sense, Read Capacity 

The governing text is the following from p.62 of -08 on the contents of 
the Response PDU: 

    3.4.6 Data Segment - Sense and Response Data Segment 

       iSCSI targets MUST support and enable autosense.  If Status is CHECK 

       CONDITION (0x02), then the Data Segment contains sense data for the 
       failed command. 

       For some iSCSI responses, the response data segment MAY contain some 

       response related information, (e.g., for a target failure it may 
       contain a vendor specific detailed description of the failure). 

Julian may be able to shed more light on the intended meaning of 
"phase collapse" for the response case, but the above text makes 
it quite clear that data transferred by the action of a SCSI command 
(including Read, Inquiry, Mode Sense, and Read Capacity) cannot be 
put in the Response PDU.  A target can send the Response PDU immediately 
following the last Data-In PDU for the associated command, which is 
similar to the ability of an Initiator to send unsolicited Data-Out 
PDUs.  There is no Target analog to the Initiator's ability to send 
Immediate Data in the same PDU as the SCSI command. 

Thanks, 
--David