RE: Towards Consensus on TCP Connections

["Douglas Otis" <dotis@sanlight.net>]

Julo,

An architecture that scales does not need to provide the entire bandwidth
from a single device.  If these devices are each handling 25 Mbytes per
second, then 2 of them exceed Fibre-Channel.  Next week you could use 4, and
the week after that 8.  The advantage of using a network without any
practical architectural restriction with intelligence at the client.  On the
other hand, you want to design a single mid-point gateway to handle the
entire bandwidth.  To what end?  You argue it can not process a TCP session
per device.  You will not be tracking mid-stream errors as this is more
costly.  You add to the burden of tracking the state of the individual
device with this mid-stream state machine requiring additional sorting due
to this merged protocol without taking advantage of TCP to aid this process.
For your type of solution, a simple hardware based tunnel would be better.
Do not include handling of the encapsulated protocol and at least it becomes
understandable and more likely to manage the task.  In other words, make it
Fibre-Channel over IP and you have a chance with your architecture.

The point to my statements was to indicate the device is able to handle an
IP interface today using Fast Ethernet as the rate from the drive is
relatively low.  Not to warm the cockles of marketing pointing to latency,
but at least they sell more drives overcoming this problem using scale.

Doug

> -----Original Message-----
> From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
> julian_satran@il.ibm.com
> Sent: Friday, August 11, 2000 2:17 PM
> To: ips@ece.cmu.edu
> Subject: RE: Towards Consensus on TCP Connections
>
>
>
>
> Doug,
>
> I am not sure that I agree with your architecture statements but I like to
> play with numbers (as most of the fellows engineers on this list probably
> do). What would be in your opinion
> reasonable requirements for command and data transfer rates for the next
> 3-7 years?
>
> I would like to decouple that discussion from architecture - data
> rates can
> scale even in a shared
> architecture as mainframe channels have shown for years.
>
> I would rather like to understand if we can meet the data rates with
> reasonable latency.
>
> Julo
>
> "Douglas Otis" <dotis@sanlight.net> on 11/08/2000 21:14:13
>
> Please respond to "Douglas Otis" <dotis@sanlight.net>
>
> To:   "Stephen Byan" <Stephen.Byan@quantum.com>, ips@ece.cmu.edu
> cc:    (bcc: Julian Satran/Haifa/IBM)
> Subject:  RE: Towards Consensus on TCP Connections
>
>
>
>
> Today's drives can deliver 320 Mbits/second of data on the outside
> cylinders.  Improvement of the mechanics comes at a high price
> with respect
> to power and cost.  The cost/volume trend takes us to a single disk which
> increases access time as read channel data rate increases.  By offering
> scaled throughput using more drives where each drive's interface bandwidth
> is restricted with respect to read channel data rates provides a system
> with
> uniform and superior performance.  The advantage of such an approach is
> found with respect to smaller random traffic.  With more devices,
> redundancy
> is easily achieved and parallel access offers a means of performance
> improvement by spreading activity over more devices.  The switch provides
> bandwidth aggregation and is not found in the individual device.
>
> An 8ms access + latency figure in the high cost drives restricts
> the number
> of 'independent' operations that average 64k byte to 100 per second or 52
> Mbit per second.  Such an architecture of 'restricted' drives would scale
> whereas the solicitated burst approach does not.  An independent nexus at
> the LUN is the only design that offers required scaling and configuration
> flexibility.  Keeping up with the read channel is a wasted effort.  In
> time,
> 1 Gbit Ethernet will be the practical solution about the time drives are 1
> inche in size.  Several Fast Ethernet disks combined at a 1 Gbit Ethernet
> client makes sense in cost, performance, capacity, reliability, and
> scalability at this point in time.  The protocol overhead should be
> addressed.  There are substantial improvements to be made to allow this
> innovation using standard adapters.
>
> The power cost to use copper 1 Gbit is high.  Firewire does not scale and
> has a limited reach.  Firewire also places scatter/gather on the drive
> together with direct access.  Doing such over a WAN will impose
> significant
> changes.  Serial ATA is nothing more than IDE through a SERDES.  The read
> channel data rate is like a drug, just say no.  It is hard not to buy
> enough
> dram to allow a proper buffer these days.  Serial ATA removes all buffers.
> Intel is just usurping any remaining electronics at the cost of
> sensitivity
> to a near by cell phone.  Fewer drives with less electronics.  What a good
> idea?
>
> Doug
>
> > -----Original Message-----
> > From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
> > Stephen Byan
> > Sent: Friday, August 11, 2000 7:07 AM
> > To: 'ips@ece.cmu.edu'
> > Subject: RE: Towards Consensus on TCP Connections
> >
> >
> > Stephen Bailey [mailto:steph@cs.uchicago.edu] wrote:
> >
> > > The gating factor for whether iSCSI succeeds is not going to be 200
> > > MB/s instead of 100 MB/s out of a single LUN.
> >
> > In general, I agree. iSCSI can succeed in the high and midrange storage
> > market without link aggregation for a single LUN. These markets can
> afford
> > 10 Gb/s links.
> >
> > As a disk device level interface, iSCSI will not succeed unless
> > it offers at
> > least 2 Gb/s by around 2002, at very low cost for the link. Note that
> even
> > Serial ATA starts at 1.5 Gb/s in 2001. Take a look at the Serial ATA
> speed
> > roadmap on slide 16 of Intel's Serial ATA presentation at WinHEC:
> > http://serialata.org/F9pp.pdf.
> >
> > One can argue the technical merits, but from a marketing
> > viewpoint, the disk
> > industry (both suppliers and customers) has long held the view that
> > interface speeds need to match the media data rate. iSCSI can try
> > to make an
> > argument that slower speeds are technically adequate, but this
> > will increase
> > the barriers to establishing iSCSI as a device interface.
> >
> > > If iSCSI works at ALL in a cost effective way that can be implemented
> > > in a disk, there'll be wild dancing in the streets and you'll all (or
> > > maybe your companies will) be rich beyond the dreams of avarice.
> > >
> > > The easier you can make it for the implementors, the more likely it
> > > will succeed.
> >
> > Disk drive companies have implemented much more complex interfaces than
> > iSCSI and TCP - e.g. fibre channel arbitrated loop. And multiple TCP
> > connections don't look very hard to implement. They just look like a
> wart.
> > But I think a necessary one.
> >
> > Regards,
> > -Steve
> >
> > Steve Byan
> > <stephen.byan@quantum.com>
> > Design Engineer
> > MS 1-3/E23
> > 333 South Street
> > Shrewsbury, MA 01545
> > (508)770-3414
> > fax: (508)770-2604
> >
>
>
>
>