Re: iSCSI: Question on StatRN usage

[julian_satran@il.ibm.com]

Mallikarjun,

StatRN implementation is MUST. Its role is to count statuses (responses)
that where sent and allow
bulk acknowledgement. As such I did not feel any need to place restrictions
and 0 is a legal value.
As the standard allows 2**32 Initiator Tags you could have 2**32 in flight
status responses (! obviously I think it will never
happen).  Obviously if you know that the target has N outstanding commands
and finished commands and it gets
from an initiator an ExpStatRN more the N distant from where it is
something is wrong!

Julo




"Mallikarjun C." <cbm@rose.hp.com> on 18/10/2000 03:58:54

Please respond to cbm@rose.hp.com

To:   ips@ece.cmu.edu
cc:
Subject:  iSCSI: Question on StatRN usage




Julian,

Could you please comment on the following on StatRN usage?  Let me
know if I am misinterpreting the draft.

Current iSCSI draft seems to allow StatRN values from 0 through
2**32-1.  It does not qualify the value of 0 as it does for CmdRNs.
Assuming that 0 is legal, how would a receiving initiator distinguish
between the target implementation that numbers (assigns StatRNs)
read data PDUs and the one that doesn't?  A StatRN of 0 in a read data
packet could be miscontrued and scoreboarded at the initiator, when
all the target was saying is that it doesn't implement StatRN for
data (assuming that 0 happens to be a legal StatRN at the moment).

Options are:
- explicitly state that StatRN value of 0 is not legal.  This is
  simple, and my preference.  A statRN of 0 in data PDUs in this case
  indicates non-implementation.
- rely on a login dialogue to call out the capability.

Even if we choose the first option, I propose introducing a login/text
key request/response through which an initiator can ask a target not
to number iSCSI data PDUs since he cannot scoreboard all the (potentially
unlimited # per each read command) data PDUs.  Note that the converse
case for target is not critical since target controls the write data
transfers
and can hope to have scoreboarding room always available.

Thanks!
--
Mallikarjun
M/S 5601
Networked Storage Architecture
HP Storage Organization
Hewlett-Packard, Roseville.
cbm@rose.hp.com