Re: iSCSI: too much recovery?

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

Jon Hall wrote:

> >2) You don't need ordering only simple acknowledgement to free resources.
> >As such per connection  is simpler to implement and maintain. You may
> >choose to do what you suggested
> >and recover by retrying but most of this group consider this too drastic.
>
> I get confused, why is per connection easier than per
> session?  The target's task state must be maintained at the
> session level.  Pushing StatSN into the connection makes per
> connection state more complicated; it now contains a subset
> of the session's task state.

StatSN needs to be on a per-connection basis. If StatSNs were on a per-session
basis, consider the following problem :

- StatSN 1 is sent out on connection 1
- StatSN 2 is sent out on connection 2

Since these 2 status' are sent on different connections, StatSN 2 could arrive
prior to StatSN 1. The initiator detects a hole in StatSN (StatSN 1 is missing)
and issues a Status SACK to request StatSN 1, whereas StatSN 1 is still on its
way to the initiator.

Also, StatSN per connection avoids sharing StatSN state across connections [and
thereby, NICs].


> >4)Logout response is there to make sure that you had an orderly close (not
> >necessarily a shutdown - e.g., take out an adapter for maintenance)  and no
> >other recovery is needed. Recall that it can be sent on a healthy
> >connection for a bad one.
>
> Assuming a healthy connection, what additional information is in
> the Logout Response pdu that is not seen by the Logout sender when
> the Logout receiver closes the connection?  Or, asked another way,
> if response=1 in the Logout Response pdu, what happens...

I agree with Jon on the logout response issue and this is the same position I
have stated earlier on this issue. The logout response adds little value and
logout can be a 1-way process with the implicit response being the target
closing the TCP connection. Initiators typically do not care about the logout
response.

IOW, Initiators typically don't care if logout response indicates "cleanup
failed".

Regards,
Santosh
begin:vcard 
n:Rao;Santosh 
tel;work:408-447-3751
x-mozilla-html:FALSE
org:Hewlett Packard, Cupertino.;SISL
adr:;;19420, Homestead Road, M\S 43LN,	;Cupertino.;CA.;95014.;USA.
version:2.1
email;internet:santoshr@cup.hp.com
title:Software Design Engineer
x-mozilla-cpt:;21088
fn:Santosh Rao
end:vcard