Re: iSCSI - Change proposal Removing the X bit

["Robert D. Russell" <rdr@mars.iol.unh.edu>]

Julian:

I vote for making the X bit reserved and leaving the I bit
and direction bits unchanged and unshifted.  This will cause
the least disruption to everything developed so far,
in our case, a lot of our testing software.
There seems to be no urgent need to "shift" the these other
bits, and there may be some future use for the unused X bit.

Thanks,
Bob Russell


On Fri, 26 Oct 2001, Julian Satran wrote:

> Dear colleagues,
> 
> We intend to publish very soon version 09 of the draft in its current
> format (not many changes) and postpone the editorial changes (already under
> way) for 10.
> 
> One of the latest change proposal involves removing the X bit.
> 
> The X bit has been used in several types of restart/replay but is somewhat
> made redundant by the removal
> of the command replay.
> 
> This involves removing the X bit from request byte 0 and either making it
> reserved or "shifting left" the rest of the general-use bits (I and the
> direction bit).
> 
> It also involves mandating a cleaning NOP.
> 
> The cleaning NOP is needed in order to "flush out" old command PDU that can
> be left over by simple sequences like the one in the following scenario:
> 
> 2 connections
> 
> On connection 1 I->T c1,c2,c3
> On connection 2 I->T c4,c5,c6
> 
> Targets receives everything and acts on commands but responses are sluggish
> and initiators sees only an ack for
> c1.  It then retransmits c2, and c3 while there answer are in flight back
> after which the connection is almost dead and not used by initiator.
> 
> After a complete wrap around, involving only connection 2,  the target
> suddenly gets c2, c3 in a correct window and acts on them.
> 
> The need to clean-up old PDUs is common to all protocols that use a
> sequence that wraps and we suggested cleaning up using a NOP.  We will
> mandate a cleaning NOP only on connections that had at least one "retry".
> 
> It looks like we might e able also to abandon the task management -
> reassign function and do it with a reissue (with the same NOP cleanout
> implication) since retiring the replay function makes the reassign
> unambiguous (reissuing a command, after logout, on a new connection -
> implies reassign).
> 
> Please comment - I need your input urgently.
> 
> Julo
> 
> 
>