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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: iSCSI ERT: data SACK/replay buffer/"semi-transport"> >Santosh, > >I can't find the place where this is stated. SNACK as a PDU type is >mandated. But it can be rejected outright. Sorry, you agreed that status SACK is mandatory in ERT forum last week in response to my comments. Has there been a change in your opinion? Attached is the email in a long email thread (issue 3) where you agreed to make this explicit in rev06. -- Mallikarjun Mallikarjun Chadalapaka Networked Storage Architecture Network Storage Solutions Organization MS 5668 Hewlett-Packard, Roseville. cbm@rose.hp.com >1.2.2.2 show explicitely that SACK can be rejected. We can add a protocol >specific parameter in the target Logical Unit Control Page (non-setable) by >which the target will indicate support for SNACK. > >Julo Santosh Rao <santoshr@cup.hp.com> on 04/04/2001 23:53:32 Please respond to Santosh Rao <santoshr@cup.hp.com> To: Julian Satran/Haifa/IBM@IBMIL cc: Jon Hall <jhall@emc.com>, ips@ece.cmu.edu Subject: Re: iSCSI ERT: data SACK/replay buffer/"semi-transport" julian_satran@il.ibm.com wrote: > > Jon, > > Inexpensive implementation are always free to do away with recovery. That > si true for targets too. That's not the interpretation one gets from reading the spec and prior discussions on this list. Per the spec, support for Status SACK is mandatory while support for data SACK is optional. IOW, targets MUST retains state information to satisfy a potential status SACK request. - Santosh ------------------------------------------------------------------------------ From julian_satran@il.ibm.com Tue Mar 27 05:16:54 PST 2001 Received: from mailhub.rose.hp.com (mailhub.rose.hp.com [15.96.64.24]) by core.rose.hp.com with ESMTP (8.8.6 (PHNE_14041)/8.8.6 SMKit7.02) id FAA26277 for <cbm@core.rose.hp.com>; Tue, 27 Mar 2001 05:16:52 -0800 (PST) From: julian_satran@il.ibm.com Received: from atlrel2.hp.com (atlrel2.hp.com [15.10.184.10]) by mailhub.rose.hp.com with ESMTP (8.7.1/8.7.3 SMKit7.02) id FAA10600 for <cbm@rose.hp.com>; Tue, 27 Mar 2001 05:15:51 -0800 (PST) Received: from d06lmsgate.uk.ibm.COM (d06lmsgate.uk.ibm.com [195.212.29.1]) by atlrel2.hp.com (Postfix) with ESMTP id AFC11120 for <cbm@rose.hp.com>; Tue, 27 Mar 2001 08:15:49 -0500 (EST) Received: from d12relay01.de.ibm.com (d12relay01.de.ibm.com [9.165.215.22]) by d06lmsgate.uk.ibm.COM (1.0.0) with ESMTP id NAA50078; Tue, 27 Mar 2001 13:55:50 +0100 Received: from d12mta02.de.ibm.com (d12mta02_cs0 [9.165.222.253]) by d12relay01.de.ibm.com (8.8.8m3/NCO v4.95) with SMTP id PAA174358; Tue, 27 Mar 2001 15:09:58 +0200 Received: by d12mta02.de.ibm.com(Lotus SMTP MTA v4.6.5 (863.2 5-20-1999)) id C1256A1C.00483A46 ; Tue, 27 Mar 2001 15:08:55 +0200 X-Lotus-FromDomain: IBMIL@IBMDE To: cbm@rose.hp.com Cc: someshg@yahoo.com, steph@cs.uchicago.edu, hufferd@us.ibm.com, cbm@rose.hp.com, ldalleore@snapserver.com, Venkat Rangan <venkat@rhapsodynetworks.com>, Black_David@emc.com Message-ID: <C1256A1C.0048399C.00@d12mta02.de.ibm.com> Date: Tue, 27 Mar 2001 15:12:01 +0200 Subject: Re: iSCSI ERT: error recovery comments Mime-Version: 1.0 Content-type: text/plain; charset=us-ascii Content-Disposition: inline Status: RO Comments in text. Thanks Julo "Mallikarjun C." <cbm@rose.hp.com> on 27/03/2001 01:41:48 Please respond to cbm@rose.hp.com To: cbm@rose.hp.com, someshg@yahoo.com, steph@cs.uchicago.edu, Julian Satran/Haifa/IBM@IBMIL, John Hufferd/San Jose/IBM@IBMUS cc: Black_David@emc.com Subject: iSCSI ERT: error recovery comments Hi Julian and the Team, Here are some comments on error recovery issues. I hope these will be addressed soon. Thanks. 1. The draft should clearly state that if a target doesn't support retry (replay in my previous memo's terminology), it must not silently accept a command with retry bit and re-do the I/O. 2. Consequent to the above - - Clarification required on section 6.7.1, page 83, last para. Please confirm and clarify in the draft: If the target sends a response with an iSCSI error response of "SACK-rejected" that implicitly terminates the task - no retries are allowed. If the target sends a Reject PDU with "Data SACK Reject" code, the task stays open and the initiator may try to recover using SACK/retry. +++ I will clarify it will read: An iSCSI target MAY reject a data-SNACK and terminate the command with an iSCSI command response of SNACK rejected. In this case, the task is terminated and no future action is expected at target and initiator. Alternatively, an iSCSI target MAY reject a data-SNACK with a reject response of data SNACK rejected. In this case the task is still open and may be recovered using the retry. +++ - On a data digest error on a data PDU without the F-bit, the draft states that the target must wait for a data PDU with the F-bit (per section 6.2), then a command termination is signalled with a Reject PDU! I like the formulation in 2.4.2 better. I strongly recommend that similarly, the target shall send a SCSI Response with a iSCSI response of "delivery subsystem failure". In general, I suggest that anytime a target terminates a task internally, it must generate a SCSI Response PDU with an appropriate response code. +++ It reads now: When a target receives an iSCSI PDU with a header digest error or a payload digest error in an iSCSI PDU, it MUST answer with a Reject iSCSI PDU with a Reason-code of Header-Digest-error or Data-Digest-Error and discard the offending PDU. If the error is a Data-Digest-Error in a Data-PDU, the target MUST either request retransmission with a R2T or answer with a command response PDU with a response-code of delivery-subsystem-failure and abort the task. If the target is answering with an error in the command response PDU it must wait for the target to receive all the data (signaled by a Data PDU with the final bit Set for all outstanding R2Ts) the command response PDU. ++++ 3. While the following is implied in different sections, it is not obvious. Please clarify the following in the draft - "Status SACK support is mandatory, whereas data SACK support is not." +++ will do in 2.16.1 +++ 4. The general policy of retry should be that all ordered commands shall support retry bit, since the loss of an ordered command creates a hole in target scoreboarding and stalls the target pipeline. Retry hopefully can plug the hole quickly to avoid this. 5. As a fallout of the above comment, Retry bit must be supported for Text Commands. +++ I have added the X-bit. The reason I did no earlier was that I could not foresee a case in which the command is not idempotent - I can allways be resent - but I guess it is cleaner with the X +++ 6. Section 2.20, page 71 on Reject must specify if a retry of the operation is allowed for each Reject PDU reason code. Lack of specification could lead to interoperability issues down the road with "retry wars" raging between heterogeneous implementations (ex., target rejects the retry bit, initiator retries the "retry" bit,....). +++ the part now reads: The reject Reason is coded as follows: 1 - Format Error 2 - Header Digest Error 3 - Data (payload) Digest Error 4 - Data-SNACK Reject 5 - Command Retry Reject 15 - Full Feature Phase Command before login Some of the reject reasons terminate or prevent the creation of a task at the target and no retry is possible in those cases. Format error for a command, Command Retry Reject and Full Feature Phase Command before login are in this category. 7. NOP-OUT does not require CmdSNs. Why make it an ordered command and run the risk of a digest error on it leading to a hole in command ordering? +++ the reason I wanted it ordered is to check the whole command path - but you may try to convince me that it is not a good idea +++ -- Mallikarjun Mallikarjun Chadalapaka Networked Storage Architecture Network Storage Solutions Organization MS 5668 Hewlett-Packard, Roseville. cbm@rose.hp.com
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