RE: iSCSI: Clarification (again) for Task Management Commands

["Somesh Gupta" <somesh_gupta@silverbacksystems.com>]

Julian,

Section 9.4 does (or so I can figure)
leave the sort of hole mentioned
below uncovered. On a multiple connection session,
the status for any of the commands effected by
the task management command could already be in
transit on any of the connections by the time the
task management command is received by the target,
and its reception is acknowledged - and then
received by the initiator.

The barrier works well for a single connection
because the command sequence number for the task
management command makes sure that there is nothing
stuck in the "pipe". However, there could be status
"stuck" in the other pipes.

The mechanism David indicated might be the only
way to be sure, which however might require a NOP
on each connection to ensure there is nothing
in the pipe.

Somesh

> -----Original Message-----
> From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
> Sent: Saturday, November 10, 2001 7:26 AM
> To: somesh_gupta@silverbacksystems.com
> Subject: RE: iSCSI: Clarification (again) for Task Management Commands
>
>
> Read 9.4 for one implementation - Julo
>
>
>
>
> "Somesh Gupta" <somesh_gupta@silverbacksystems.com>
> Sent by: owner-ips@ece.cmu.edu
> 10-11-01 05:26
> Please respond to somesh_gupta
>
>
>         To:     <Black_David@emc.com>, <ips@ece.cmu.edu>
>         cc:
>         Subject:        RE: iSCSI: Clarification (again) for Task
> Management Commands
>
>
>
> David,
>
> In iSCSI the multiple connection/session construct
> adds significant complexity in determining whether
> a response for a command (on a different connection
> than the one on which the task management command
> was sent) impacted by the task management command will
> be received or not - and when?
>
> On a single connection, or similar links, when the
> response for the task management command is
> received (or after a fixed additional time), no
> responses will be received for the commands aborted
> by the task management command.
>
> However, with multiple connections there is no
> such "flushing" event on connections other than the
> one on which the task management command was sent.
>
> I would hope that the protocol would address this
> situation - the current response seems to be be to
> put the task tag and some associated resources in
> a zombie state for an unspecified amount of time.
>
> Somesh
>
>
> > -----Original Message-----
> > From: Black_David@emc.com [mailto:Black_David@emc.com]
> > Sent: Friday, November 09, 2001 6:53 PM
> > To: somesh_gupta@silverbacksystems.com; ips@ece.cmu.edu
> > Subject: RE: iSCSI: Clarification (again) for Task Management Commands
> >
> >
> > Somesh,
> >
> > The language in question reflects fairly direct requirements
> > language to be found in SAM-2's description of SCSI Task Management.
> > FCP goes to serious lengths with FC sequence aborts to make sure
> > this behaves as required.
> >
> > For iSCSI, if responses to the aborted commands show up unexpectedly,
> > they have to be discarded.  How the Initiator keeps track of that
> > is the Initiator's problem - keeping track of the CmdSN of the
> > Abort Task Set may be useful.
> >
> > --David
> > ---------------------------------------------------
> > David L. Black, Senior Technologist
> > EMC Corporation, 42 South St., Hopkinton, MA  01748
> > +1 (508) 435-1000 x75140     FAX: +1 (508) 497-8500
> > black_david@emc.com       Mobile: +1 (978) 394-7754
> > ---------------------------------------------------
> >
> > > -----Original Message-----
> > > From: Somesh Gupta [mailto:somesh_gupta@silverbacksystems.com]
> > > Sent: Friday, November 09, 2001 4:55 PM
> > > To: IPS
> > > Subject: iSCSI: Clarification (again) for Task Management Commands
> > >
> > >
> > > Resend to add iSCSI tag. Sorry for missing it.
> > >
> > > On page 67 of the 8-92.txt draft (section 3.5.1), it
> > > says
> > >
> > > "For all the tasks covered by the task
> > > management response (i.e., with CmdSN not higher than the task
> > > management command CmdSN), additional responses MUST NOT be delivered
> > > to the SCSI layer after the task management response."
> > >
> > > If there is a multiple connection session,
> > > a status for a command impacted by the task
> > > management command (say ABORT TASK SET) could
> > > be stuck in the pipe on one connection, while
> > > the ABORT TASK SET completes on another
> > > connection.
> > >
> > > How does the initiator iSCSI enforce the rule above?
> > > Seems to be the equivalent of sending the impacted
> > > commands on other connections in a zombie state,
> > > and not having a very good idea of how to get out.
> > >
> > > Similarly Section 9.4 provides additional rules,
> > > but seems to leave a hole open with regards to
> > > status already in flight on other connections.
> > >
> > > Any clarifications would be appreciated.
> > >
> > > Somesh
> > >
> >
>
>
>
>