Re: IETF mailing list question on Storage over Ethernet/IP
Thank you all for some excellent discussions on the subject. For all the
reasons mentioned, I am mapping TCP/IP to DWDM to create very high performance
SANs. I hope to share more on this as we progress and launch products. You
can see more on this at www.lightel.com.
On Fri, 26 May 2000, Dave Nagle wrote:
A few comments about this one.
1. FC does not provide reliable transmission. It provides for error
detection, but escalates recovery to "upper level protocol". FCP-2 has
improved this situation, but is not widely implemented yet. One of the
advantages of using a transport such as TCP is that link errors will be
corrected in a manner that is transparent to the application protocol
2. Jumbo frames will not be necessary when TCP is implemented in hardware.
Most FC implementations use 1024 byte frames, and performance is very
adequate, given hardware implementation of FCP.
3. The cost of using different transport protocols in the LAN and WAN is
that the two will not interoperate. Many of us believe that TCP has proven
itself in both the LAN and WAN. I bet your PC or UN*X workstation is using
TCP for all its protocol needs.
4. The IPS working group is mapping SCSI to TCP. Another working group is
mapping FC to IP. These are very different approaches. The first (ours)
preserves SCSI, but does not include any vestige of Fibre Channel. It is
intended for use in the LAN, MAN and WAN. Its best use is for connecting
hosts computers to storage controllers using Ethernet and IP WAN technology.
It will be possible, but non-trivial, to translate between SCSI over TCP/IP
and SCSI over Fibrechannel. The second is a tunneling scheme for extending
Fibre Channel over the IP WAN. It does not contemplate Ethernet-based hosts
or storage controllers.
5. Just about any reliable transport will do nicely for transporting SCSI
commands. We chose TCP because its implementation and behavior are
well-known, and it is well-supported with load-balancing, QoS and security
features. While another protocol (such as reliable datagram) might be
arguably better suited to storage transport applications, we'll use TCP
"because it's there". We'll have the benefit of all the other investment
that's going into improving TCP for internet uses.
Networked Storage Architecture
tel: +1 916 785 4578
fax: +1 916 785 1911
From: Dave Nagle [mailto:bassoon(_at_)yogi(_dot_)ece(_dot_)cmu(_dot_)edu]
Sent: Thursday, May 25, 2000 4:29 PM
To: SCSI-over-TCP List
Subject: IETF mailing list question on Storage over Ethernet/IP
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Date: Thu, 25 May 2000 19:27:02 -0400
From: Dave Nagle <bassoon(_at_)yogi(_dot_)ece(_dot_)cmu(_dot_)edu>
To: "Jon William Toigo" <jtoigo(_at_)IntNet(_dot_)net>
Subject: Re: Storage over Ethernet/IP
>> I am seeking a few points of clarification:
>> 1. Fibre Channel folks have attempted to explain to me
why TCP/IP could =
>> NEVER be a viable interconnect for block level storage
operations. They =
>> a. TCP is too CPU intensive and creates too much latency
for storage =
>> I/O operations.
>> b. The IP stack is too top heavy and processing packet
headers is too =
>> slow to support storage I/O operations.
There is a lot of work to show that this is not true. Check out Van
Meter's 1998 ASPLOS paper "VISA - Netstations virtual internet SCSI
Perhaps more importantly, there are many companies that are building
TCP in silicon ASICs. This should make TCP's performance comparable
to Fibre Channel. Both TCP/IP and FC provide about the same
functionality ... reliable, in-order transmission.
The bottom line is that FC is done in hardware while TCP has
traditionally been done in software. Therefore, previous performance
numbers are not going to be fair. Once TCP is in silicon, its
performance should be roughly equal to FC.
>> c. The maximum throughput of a GE TCP/IP connection is
768 Mps, which =
>> is too slow to support storage I/O operations.
I believe there are higher numbers (especially with Jumbo
Frames). Alteon's web site show's 920 Mbps. Microsoft and Duke
University have both shown TCP performance o 1Gb+/s performance over
BTW, why is 768 Mbps too slow for storage. Many apps (e.g.,
transaction workloads) are I/O's per second bound, not bandwidth
bound. Also, even if storage over IP/ether is a bit slower than FC,
the benefits of leveraging IP's infrastructure (i.e., routers,
switches, NICs, network management, networking people) is a huge
There is also the issue of SCSI over TCP/IP in the SAN vs. the
LAN/WAN. Some companies, focusing on the SAN, are building
SCSI/lightweight transport/IP while others, focusing on the WAN,
propose SCSI/TCP/IP. It may be the case that SAN and WAN traffic use
different transport protocols to gain a bit of extra performance in
>> Is any of this true?
>> 2. Adaptec has posited a replacement for TCP called STP
for use as a =
>> transport for storage. Does anyone know anything about this?
From Paul von Stamwitz's posting to the ips mailing list ...
The link to the SEP draft is
The press release is at:
The demo shows a Gb ethernet controller transporting SCSI
traffic to several
targets through an off-the-shelf 100TX switch with a Gb
uplink. The targets
are ethernet to U160 SCSI bridges with one or more SCSI
drives attached. The
host controller runs under NT4.0 at appears to the OS as
a SCSI host bus
The architecture is based on Adaptec's SCSI Encapsulation Protocol
(SEP). SEP is mapped on top of TCP/IP or a light-weight transport
protocol specifically designed for SANs.
An SEP overview was presented at the IPS BOF in Adelaide
last month and an
internet draft on SEP was submitted to IETF this week. I
will forward the
link as soon as it becomes available. This draft is informational
only and intended to aid in this group's work toward an industry
standard SCSI transport protocol over IP networks.
>> 3. Current discussions of the SCSI over IP protocol seem
to ignore the =
>> issue of TCP or any other transport protocol. Does anyone know =
>> definitively what transport is being suggested by the
Current SCSI over IP discussions are not ignoring TCP ... they are
definitely considering TCP as the primary transport. See the ips
web site at:
>> 4. Another storage company is looking at Reliable UDP as a substitute =
>> for TCP in storage data transfers. Where can I learn more about this =
>> protocol, which I am told was introduced many years ago by Cisco?
Companies to look at include:
Also, I believe that the IETF IP over FC working group is now
looking at FC over IP.
Director, Parallel Data Lab
Senior Reseach Computer Scientist
School of Computer Science
Carnegie Mellon University
Pittsburgh, PA 15213
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