Re: rationale to send PDUs in increasing CmdSn onsingle connection
yes it is must and besides being pointless
sending out of order would break some assumptions about detecting missing
items (as Pat has nicely outlined in her note).
||William Studenmund <wrstuden@xxxxxxx>
||Eddy Quicksall <Quicksall_iSCSI@xxxxxxxxxxxxx>
||Parav Pandit <paravpandit@xxxxxxxxx>,
Julian Satran/Haifa/IBM@IBMIL, Ips <ips@xxxxxxxx>
||Re: rationale to send PDUs in
increasing CmdSn onsingle connection|
On Oct 19, 2007, at 8:03 AM, Eddy Quicksall wrote:
Julian, below you said "no" to #2. But is there
a restriction in the RFC (maybe I just don't remember it)? I agree it has
no practical value but I have used it to test my re-ordering logic with
only one connection.
Parav quoted a MUST from the RFC on this, so I'd call
that a restriction. :-)
I agree that it's a reasonable thing to do to test re-ordering
logic. But I think that test environments don't count in that to be a good
test of error handling, they _must_ break the spec. :-) Otherwise it's
exceptionally difficult to reproducibly test how devices handle error conditions.
---- Original Message -----
Sent: Friday, August 31, 2007 11:53 AM
Subject: Re: rationale to send PDUs in increasing
CmdSn onsingle connection
Parav Pandit <paravpandit@xxxxxxxxx>
wrote on 31/08/2007 12:52:04:
> RFC 3720, section 220.127.116.11 says
> "On any connection, the iSCSI initiator MUST send the
> commands in increasing order of CmdSN, except for
> commands that are retransmitted due to digest error
> recovery and connection recovery. "
> (Assuming Single TCP connection ISCSI session)
> 1. I interpret above 18.104.22.168 statement as
> SCSI layer gives SCSI commands to the ISCSI stack in
> the order of Cmd-1 and Cmd-2.
> Cmd-1 will have CmdSn = 10.
> Cmd-2 will have CmdSn = 11.
> ISCSI stack CAN send PDUs to the TCP layer in
> following order ONLY.
> PDU-1 with Cmd-1.
> PDU-2 with Cmd-2.
> Is this correct interpretation?
> 2. On a SINGLE connection can ISCSI stack send the
> PDU-1 with Cmd-2 followed by
> PDU-2 with Cmd-1?
> Assuming the answer of the question #2 is No,
> 3. If there are multiple connections in a session then
> command MAY any way reach out of order. And targets
> need to wait for the previous expected commands.
> So targets will receive out of order ISCSI PDUs from
> the TCP layer and ISCSI stack handles them.
> So then why initiators have restriction of sending
> command in the increasing order of CmdSn on SINGLE TCP
To simplify recovery and to...
> Is it to simplify the implementation of targets
> supporting only single TCP connection?
and there was no visible motivation for out of order commands on a single
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