iSCSI: Use of the A bit

[Eddy Quicksall <Eddy_Quicksall@ivivity.com>]

Here is a case that I want to go over and if there is not already a solution, I think a refinement to the A bit could solve it.

 

The problem is that a target (perhaps an iSCSI disk drive) does not have enough memory to transfer the full READ request so it must read from the medium as much as it can, transmit that, when that transmission is known to be good, read the next bunch, transmit that and so on.

 

The problem we have is that the target must keep the buffer around until the transfer has been "ack'd" via ExpStatSN. But that status can't be sent because all of the requested data has not been sent. So the target would have to refuse to do the command.

 

I was going to use the A bit for this thinking it would force the initiator to give an "ack" but our current wording does not make this a sure fire thing:

 

1) The initiator may not want to run at ErrorRecoveryLevel 1.

2) The initiator may ignore the A bit if it deems that the bit is being set aggressively.

3) The target may set the A bit no more frequently than MaxBurstSize.

 

Comments?

 

mailto:Eddy_Quicksall@iVivity.com