Re: summary of iSCSI meeting 22 June 2000

[Matt Wakeley <matt_wakeley@agilent.com>]

julian_satran@il.ibm.com wrote:

> For all those concerned about the recovery discussion here are some
> clarifications:
>
> 1. The whole discussion thread was related to an attempt to recover from
> one TCP connection failure
> in a session that has multiple TCP connections in order to fully exploit
> the fault tolerance level users are expecting when using several
> connections

Agreed.


> 2. As we are aware that stateful devices and operation idempotency are hard
> to handle in general terms
> we are currently contemplating mostly recovery mechanisms that are
> "target-centric" (mostly target initiated).

That's not the way I understand it.  Targets are (generically) dumb devices and
only do what they're told.  It is the initiator's responsibility to recover the
device/connection.  Not the target's responsibility to recover the initiator.

This is the way FCP-2 performs error recovery.  The only thing the target does
is "logout" an initiator if a master timeout expires (see RR_TOV).

-Matt


> Obviously we would love to be able to recreate a TCP connection
> in exactly the state it got lost
> but we are not aware of any such magic being available...
>
> Julo
>
> Julian Satran - IBM Research Laboratory at Haifa
>
> David Robinson <robinson@ebay.sun.com> on 22/06/2000 20:30:05
>
> Please respond to David Robinson <robinson@ebay.sun.com>
>
> To:   Kalman Meth/Haifa/IBM@IBMIL
> cc:   ips@ece.cmu.edu, scsi-tcp@external.cisco.com (bcc: Julian
>       Satran/Haifa/IBM)
> Subject:  Re: summary of iSCSI meeting 22 June 2000
>
> meth@il.ibm.com wrote:
>
> > Further discussion of what happens when TCP packets get lost, especially
> if
> >  they contain an iSCSI header.
> > How well can iSCSI compete with FC if we are so dependent on TCP, with
> its
> > dropped packets.
> >
> > In the LAN, TCP packets are not generally lost and we should be
> comparable
> > to FC.
> > Over WAN, can have packet loss and resulting complications, but that is
> no
> > longer competing with FC
> > (which doesn't exist at all in the WAN).
>
> Huh? TCP packets can never get lost, you either get the packet
> or the connection is dropped.  There may be some delay as TCP
> performs a retransmission which will be rare on LANs and not
> so rare on WANs. I don't see how this is a FC vs TCP issue.
>
>      -David