Re: iSCSI-related conclusions from Orlando interim Meeting

[Santosh Rao <santoshr@cup.hp.com>]

> - Abort WARNING will be added to the draft.
> - Immediate Delivery of Aborts and similar task management commands
>   may have unexpected results when multiple TCP connections are in use
>   because Abort, Clear Task Set, etc. may bypass command(s) to be
>   aborted/cleared on other TCP connections.
> - Ordered Delivery should be used instead when this is a concern.

Is the above referring to ordered delivery as in CmdSN based ordering or
the use of the Ordered Task Tag ?

I see the following issues with this :

a) CmdSN defines the order of delivery from the iSCSI layer to the SCSI 
   ULP at the target. 
   
   Abortion of active tasks will involve the invalidation of the 
   SCSI State information [being accessed by either adapter micro-code 
   or the FPGA/ASIC] maintained for these tasks. 
   This process is kicked off in the iSCSI layer and this abort 
   functionality in the iSCSI layer will also need to be subject to the 
   ordering constraints of CmdSN. (in addition to the ordering of delivery 
   to the SCSI ULP).

b) A received Task Management command [on, say, connection 'x'] 
   cannot be performed due to previous CmdSNs not yet
   having arrived. (In the case where another connection 'y' in the 
   session is faulty and CmdSNs sent on connection 'y' have'nt arrived).

c) Ordered Task Tags should not be used with error recovery Task
   Management commands, since this can result in a deadlock of the task
   mgmt command in case the older tasks are'nt completing in the SCSI ULP
   due to some ULP problem. ("An Ordered Task cannot enter the enabled
   state until all older tasks have completed.")

d) Given that Immediate command delivery (CmdSN of 0) is un-usable for
   task management commands, is there any other application for this 
   feature? If not, all references to it can be removed from the draft and
   CmdSN can start from 0.

Regards,
Santosh

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Santosh Rao
Software Design Engineer,
HP, Cupertino.
email : santoshr@cup.hp.com
Phone : 408-447-3751
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