----- Original Message -----
Sent: Wednesday, April 25, 2007 11:04
AM
Subject: Re: FW: Recent comments
about FCoE and iSCSI
Eddy,
That is oversimplified and ignore the drop rate
assumption and error rate assumptions made in FCP(FCP has no transport layer).
To get to it on a sizable network requires more than PAUSE.
Julo
Basically, it is sending FC frames over Ethernet. This
localizes the traffic unless you route based on MAC addresses. So you send
2146 bytes of FC frame plus 18 bytes of Ethernet overhead as FCoE ?standard?
packet. 18 bytes of Ethernet gets stripped and you have straight FC frame that
can go through any FC network. Now you can have 10G Ethernet pipes into
existing FC SANs. Limited market potential as far as I can see. The key
argument is it much easier to implement than iSCSI and also has less overhead
and uses all the benefits of FC. End to End credits are simulated using PAUSE
command on Ethernet and MAC addresses are mapped into WWNs.
Biggest knock is that it will not
route on the ?global? scale like TCP/IP would.
Eddy
-----
Original Message -----
From: Julian
Satran
To:
John
Hufferd
Cc:
ips@xxxxxxxx
Sent: Wednesday, April 25, 2007 8:09 AM
Subject: Re: FW: Recent comments about FCoE and
iSCSI
"John
Hufferd" <jhufferd@xxxxxxxxxxx> wrote on 25/04/2007 02:45:51:
> Julian,
> To be
sure you understand our position; Brocade is pushing iSCSI as an
>
outreach protocol from the Data Center. We also believe iSCSI is very
>
useful for installations that do not have a Fibre Channel
>
infrastructure, and in that case we will be able to sell them our new
>
iSCSI and TOE offload HBAs.
>
> When I say iSCSI is an
outreach protocol, this is a statement that iSCSI
> is very important to
connect "stranded" servers to the Fibre Channel
> Fabric. That is,
we sell iSCSI-to-FC Gateway devices which will permit
> iSCSI Servers
(software or HBA iSCSI initiators) to connect to the
> Enterprise "Bet
Your Business" FC Storage. This of course also applies
> to
Desktops and Laptop systems, and systems at distance.
>
You make it sound
like:
1.
most of the servers in the
world have their storage on the network - and that is not the
case
2.
FCP is basically better
performing than iSCSI - and that is not true either
3.
Gatewaying is expensive - and it is perhaps so
but only if you are completely relying on FCP storage (and there are plenty of
good iSCSI vendors of storage)and pushing the price on the servers is not
cheap either - at least not for the server buyer
> Now with that positioning, it is important to understand the
limitation
> to this strategy. The primary problem is that iSCSI
to FC Bridging
> (Gatewaying) is relatively expensive (compared to
simple FC
> connections). Though we have some of the best priced
Gateways on the
> market, it is not cost feasible to replace all the
server connectivity
> to FC storage with iSCSI for the hundred to
thousands of servers in the
> Data Center. And since, if there is
to be a consolidated Network
> connection to the servers in the Data
Center, there must be an
> evolutionary replacement of Server
Connections to Storage. That means
> there must be a
bridge/Gateway approach. And as I mentioned before,
> there is
just too much cost in the iSCSI to FC Gateway.
>
> The issue is
the server requirement to have a single connection type to
> handle
cluster messaging, general messaging, and storage. iSCSI is
>
clearly an option for the storage, however, the gateway costs are too
>
high for iSCSI to be used as the "normal" server connect into a FC
based
> Fabric. That is true for the current 1GE; and for 10GE the cost
is just
> out of sight. The reason for this is the requirement for
TCP/IP
> termination and re-initiation with FC at the Gateway.
>
> Now with respect to FC over Ethernet the important thing to
understand
> is that it is not Ethernet as we have known it up to know.
The Ethernet
> we are talking about is a type of Ethernet that can
only be deployed in
> a constrained environment such as a Data Center.
This form of Ethernet
> is called DCE (Data Center Ethernet) or
CEE (Convergence Enhanced
> Ethernet). This form of Ethernet is a
Loss-less type Ethernet, with
> multi-priority and Flow Control.
This is NOT an Internet or Intranet
> type of Ethernet.
>
> FCoE is all about using the DCE (CEE) to carry FC frames. The
rest of
> the Host and storage stack remain the same, the functions and
features
> of the switches also remain the same and add the capability
to provide
> Cluster Message Switching which has latency close to
InfiniBand speeds.
>
>
> Because the FC frames are
transported to the switches intact via a DCE
> frame, the Bridging, if
you want to call it that, is virtually non
> existent. Hence you
can deliver the FC frames to FC devices, or send FC
> frames to DCE FCoE
devices, just like one would do if it was all FC. And
> all this is done
while performing Cluster message switching and general
> message
trucking to the IP outfacing network.
>
The rosy future of the yet to appear
DCE/CEE and a layer 2 only world.
First you have some terms confused:
Bridging is the term commonly used for Layer-2
switching and routing is therm used for layer-3 (switching).
Bridging has some advantages (less
management) that have created a movement towards an enterprise
wide
LAN. But this has a
long way to go and will require significant equipment and protocol
changes.
Even its
proponents do not call for transportless networks, lossless networks
etc.
The second trouble
with your argument is that there are no known large scale networking
technologies that
really
work at full speed (high speed) and are lossless (flow-controlled) and
errorless like FCoE assumes.
The TCP/IP has solved this issue for every generation using the
proven end-to-end principle (and is doing so now).
And it is not by chance so and that is why all
networking applications are built above layer-3 and not dropping layer-3 (like
FCoE) does.
Although
I can understand the DCE arguments as a management statement I would prefer
like any rational engineer, to base my building blocks on structures that are
proven and long lasting. And those are still the end-to-end TCP/IP that can
accommodate even your FCP addicts. The IPS TWG has developed the iFCP that
does exactly what FCoE claims to do an a better base.
> This means an evolutionary process is
possible to the solution of
> getting a single Fabric connection for all
networks connected to a
> server, further, the process has very low
interconnection cost on the
> Data Center Fabric. And it maintains all
the FC Fabric Services, and all
> the same Storage Management processes.
>
> By the way, this is primarily a Server driven value
statement, there
> seems to be little value in having FCoE on the
storage controller.
> Therefore FC storage controllers (and FICON) will
be the very last
> things that connect using FCoE and that evolution
will take at least a
> decade or more.
>
It is server cost statement. It costs
nothing to connect a modern server to ethernet it will cost a bundle to
connect to FCoE and it will force users in short lived bad
solutions.
>
We see value in offering switches and Directors that can support DCE
>
switching, FC switching as well as iSCSI interconnect, and the
>
"Trunking" of general messaging to the Outfacing IP network. That
said;
> we do not see FCoE going beyond the constraints of the Data
Center.
Data Centers
now grow to tens of thousands of nodes. There is no layer-2 technology for
errorless/lossless operation at this scale and there is no good reason to
pursue one. The only possible reason (good reason) is the bridging
infrastructure but that infrastructure has a completely different rationale
than the flowcontrol.
> This issue and message is quite different from the issues
and messages
> we struggled with when we started iSCSI. There is a
consortium of folks
> both working on the DCE (CEE) and the FCoE.
Without the DCE the FCoE
> will not happen.
>
> None of the above cancels out the value of iSCSI in numerous
>
environments.
>
>
iSCSI is good for all environments. Business consideration (and
some politics) keep it form "exploding" and large storage vendors are
completely indifferent to the network connection they are using.
You and I
have also slightly different views of DCE. I expect DCE (that still has a way
to go) to improve the QoS in the data-center (and for storage too). You expect
it to bring the loss rates down to the levels that FCP assumes (FCP has no
transport layer) and that is probably a pipe dream. Todays transport solution
for loss mitigation are far more cost effective - and that's why iFCP is a
better proposition as a transition technology than FCoE and iSCSI with
gateways is propably better in the long run.
>
> .
> .
> .
>
John L Hufferd
> Sr. Executive Director of Technology
>
jhufferd@xxxxxxxxxxx
> Office Phone: (408) 333-5244; eFAX: (408)
904-4688
> Alt Office Phone: (408) 997-6136; Cell: (408)
627-9606
>
> -----Original Message-----
> From: John
Hufferd
> Sent: Tuesday, April 24, 2007 12:57 PM
> To:
'Julian_Satran@xxxxxxxxxx'
> Subject: Re: Recent comments about
FCoE and iSCSI
>
> Julian,
> I think you are wrong on this
one. The arguments are quite different
> then the ones we had in
pre iSCSI days. (By the way I missed you on
> today's Renato
meeting/conf call where Brocade took the IBM technology
> group through
FCoE as it is being placed in our plans).
> I will send you more
info when I get to my computer. But you probably
> were sent the
Brocade charts. Please review them and I will follow up
> with
more information.
> This does NOT replace iSCSI it applies only to a
DataCenter envuornment
> with lossless DCE ethernet.
>
--------------------------
> John L. Hufferd
> Sr. Ex. Director of
Technology
> Brocade Communications Systems, Inc.
> Phone: (408)
333-5244
> Mobile: (408) 627-9606
> eMail:
jhufferd@xxxxxxxxxxx
> (Sent from my BlackBerry Wireless)
>
>
> ----- Original Message -----
> From: Julian
Satran <Julian_Satran@xxxxxxxxxx>
> To: ips@xxxxxxxx
<ips@xxxxxxxx>
> Sent: Tue Apr 24 12:10:29 2007
> Subject:
Recent comments about FCoE and iSCSI
>
>
> Dear All,
>
> The trade press is lately full with comments about the
latest and
> greatest reincarnation of Fiber Channel over ethernet.
> It made me try and summarize all the long and hot debates that
preceded
> the advent of iSCSI.
> Although FCoE proponents make
it look like no debate preceded iSCSI that
> was not so - FCoE was
considered even then and was dropped as a dumb
> idea.
>
>
Here is a summary (as afar as I can remember) of the main arguments.
>
They are not bad arguments even in retrospect and technically FCoE
>
doesn't look better than it did then.
>
> Feel free to use this
material in a nay form. I expect this group to
> seriously expand
my arguments and make them public - in personal or
> collective form.
>
> And do not forget - it is a technical dispute - although we
all must
> have some doubts about the way it is pursued.
>
> Regards,
> Julo
>
>
---------------------------------------------------------------------
>
> What a piece of nostalgia :-)
>
> Around 1997 when a
team at IBM Research (Haifa and Almaden) started
> looking at connecting
storage to servers using the "regular network"
> (the ubiquitous LAN) we
considered many alternatives (another team even
> had a look at ATM -
still a computer network candidate at the time). I
> won't get you over
all of our rationale (and we went over some of them
> again at the end
of 1999 with a team from CISCO before we convened the
> first IETF BOF
in 2000 at Adelaide that resulted in iSCSI and all the
> rest) but some
of the reasons we choose to drop Fiber Channel over raw
> Ethernet where
multiple:
>
>
> * Fiber Channel Protocol (SCSI
over Fiber Channel Link) is
> "mildly" effective because:
>
> * it implements endpoints in a dedicated engine
(Offload)
> * it has no transport layer (recovery
is done at the
> application layer under the assumption that the error
rate will be very
> low)
> * the network is
limited in physical span and logical span
> (number of switches)
> * flow-control/congestion control is achieved
with a
> mechanism adequate for a limited span network (credits). The
packet loss
> rate is almost nil and that allows FCP to avoid using a
transport
> (end-to-end) layer
>
> *
FCP she switches are simple (addresses are local and the
> memory
requirements cam be limited through the credit mechanism)
>
* However FCP endpoints are inherently costlier than
>
simple NICs - the cost argument (initiators are more expensive)
>
* The credit mechanisms is highly unstable for
large
> networks (check switch vendors planning docs for the network
diameter
> limits) - the scaling argument
> *
The assumption of low losses due to errors might
> radically change when
moving from 1 to 10 Gb/s - the scaling argument
> *
Ethernet has no credit mechanism and any mechanism with
> a similar
effect increases the end point cost. Building a transport
> layer in the
protocol stack has always been the preferred choice of the
> networking
community - the community argument
> * The
"performance penalty" of a complete protocol stack
> has always been
overstated (and overrated). Advances in protocol stack
> implementation
and finer tuning of the congestion control mechanisms
> make
conventional TCP/IP performing well even at 10 Gb/s and over.
> Moreover
the multicore processors that become dominant on the computing
> scene
have enough compute cycles available to make any "offloading"
> possible
as a mere code restructuring exercise (see the stack reports
> from
Intel, IBM etc.)
> * Building on a complete stack
makes available a wealth of
> operational and management mechanisms
built over the years by the
> networking community (routing,
provisioning, security, service location
> etc.) - the community
argument
> * Higher level storage access over an IP
network is widely
> available and having both block and file served over
the same connection
> with the same support and management structure is
compelling - the
> community argument
> *
Highly efficient networks are easy to build over IP with
> optimal
(shortest path) routing while Layer 2 networks use bridging and
> are
limited by the logical tree structure that bridges must follow. The
>
effort to combine routers and bridges (rbridges) is promising to
change
> that but it will take some time to finalize (and we don't know
exactly
> how it will operate). Untill then the scale of Layer 2 network
is going
> to seriously limited - the scaling argument
>
>
>
> As a side argument - a performance
comparison made in
> 1998 showed SCSI over TCP (a predecessor of the
later iSCSI) to perform
> better than FCP at 1Gbs for block sizes
typical for OLTP (4-8KB). That
> was what convinced us to take the path
that lead to iSCSI - and we used
> plain vanilla x86 servers with
plain-vanilla NICs and Linux (with
> similar measurements conducted on
Windows).
> The networking and storage community
acknowledged those
> arguments and developed iSCSI and the companion
protocols for service
> discovery, boot etc.
>
> The community also acknowledged the need to
support existing
> infrastructure and extend it in a reasonable fashion
and developed 2
> protocols iFCP (to support hosts with FCP drivers and
IP connections to
> connect to storage by a simple conversion from FCP
to TCP packets) FCPIP
> to extend the reach of FCP through IP (connects
FCP islands through TCP
> links). Both have been
>
implemented and their foundation is solid.
>
> The current attempt of developing a "new-age" FCP
over an
> Ethernet link is going against most of the arguments that have
given us
> iSCSI etc.
>
> It
ignores the networking layering practice, build an
> application
protocol directly above a link and thus limits scaling,
> mandates
elements at the link layer and application layer that make
>
applications more expensive and leaves aside the whole "ecosystem"
that
> accompanies TCP/IP (and not Ethernet).
>
> In some related effort (and at a point also when
developing
> iSCSI) we considered also moving away from SCSI (like some
"no
> standardized" but popular in some circles software did - e.g.,
NBP) but
> decided against. SCSI is a mature and well understood
access
> architecture for block storage and is implemented by many
device
> vendors. Moving away from it would not have been justified at
the time.
>
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