Re: ISCSI: Urgent Flag requirement violates TCP.

["John Hufferd/San Jose/IBM" <hufferd@us.ibm.com>]

Glen,
Along with my previous note about the needs for TCP/IP offload NICs, let me
tell you how they work with the OSs.

The various vendors that are building these, are letting the iSCSI Device
Driver directly talk to the NIC, without going through the normal OS
TCP/IP.  This is very similar to the way a FC adapter are driven.

So  these vendors believe that they can use iSCSI to justify the TCP/IP
offload NIC, and that once there, the various  host TCP/IP stacks will,
over time, exploit this capability.  Whether or not, the latter happens
over time, I do not know, but I like the HW implementations for iSCSI
direct use.

.
.
.
John L. Hufferd
Senior Technical Staff Member (STSM)
IBM/SSG San Jose Ca
(408) 256-0403, Tie: 276-0403
Internet address: hufferd@us.ibm.com


Glen Turner <glen.turner@aarnet.edu.au>@ece.cmu.edu on 11/08/2000 12:29:53
AM

Sent by:  owner-ips@ece.cmu.edu


To:   Matt Wakeley <matt_wakeley@agilent.com>
cc:   ips@ece.cmu.edu
Subject:  Re: ISCSI: Urgent Flag requirement violates TCP.



Matt Wakeley wrote:
>
> Nope.  Machines today using "off the shelf" stacks utilizing 1Gbps
ethernet max out the CPU
> running the TCP/IP stack, with no processing power left over for doing
any work.  Machines
> will not be able to fully utilize the new 10Gbps links if the TCP/IP
processing is not
> offloaded out of the main kernel.

But that's an argument for iSCSI *not* using TCP services beyond the
socket API.  To use such services the general purpose
computer running TCP/IP offload would then need to change the
code in the operating system *and* the code in the ethernet adapter.

For commodity hardware you then need support from multiple
manufacturers to get a computer that will run a complaint
iSCSI client.  This is inviting maintenance issues (eg:
need to install Windoze 2002 to fix security issue, but
the driver for the particular ethernet card doesn't
work with Win2002, and you can't just use any off-the-shelf
TCP-offload card becuase you need iSCSI-socket support).

I trying not to harp on about this, but it seems to me that
people haven't thought out the software options at the client
end in the same detail that they appear to have put into
the target end.

My feeling is that if the client can't use off-the-shelf
gear then iSCSI is only going to displace Fiber Channel
and will not become a widespread network service.  For
example, ISPs attempting to add value to their service
will need to find another mechanism to offer a storage
and backup service to their customers, whereas iSCSI
could be an ideal candidate for that application.

Best regards,
Glen