RE: iSCSI : Abort Task "connection allegiance"

["Santosh Rao" <santo_rao@hotmail.com>]

>Santosh,
>The advantage of multiple connections or multiple homing is removed if 
>connection allegiance is mandated.

Doug,

Section 1.2.5 already mandates connection allegiance for all PDUs of a 
command.
("For SCSI commands that require data and/or parameter
transfer, the (optional) data and the status for a command must be
sent over the same TCP connection that was used to deliver the SCSI
command (we call this "connection allegiance").")

I believe the dis-advantages of sending different PDUs of a command over 
different connections has already been discussed and discarded due to the 
various state sharing issues as well as out-of-order issues it causes.

So, is the concern expressed about the existing MUST in the above statement 
in the draft ? Or are the comments directed towards the proposal to extend 
connection allegiance to the Abort Task as well ?

>The ability to recover from a seemingly failed connection may include a 
>request to restart using a different connection.  Such request will likely 
>be sent over a different connection if there is a desire to migrate.  
>Connection allegiance was to allow distributed state information to remain 
>isolated.  This isolation is problematic and not mandating allegiance 
>ensures there will always be a means to communicate intermediate states 
>between connections.

While the "retry" command processing at the target may involve co-operation 
across multiple NIC instances to fetch the data/status, this should be ok 
since it is the exception path. We should not attempt to optimize this path 
and affect the mainline paths. The mainline I/O paths require connection 
allegiance for a number of reasons that have been previously discussed on 
the reflector.

>Connection allegiance should only be preferred.

The lack of connection allegiance for all PDus of a command can cause 
out-of-order problems, with status PDUs arriving at the initiator ahead of 
the data PDUs.It also requires sharing I/O state information across NICs for 
the mainline paths, as compared to the current model where this is only 
required in exception paths.

Regards,
Santosh


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