RE: iSCSI/VI/TCP

["Merhar, Milan" <mmerhar@pirus.com>]

Costa,

Thanks for your comments on the value of using VI as part of the
iSCSI solution.  I was pretty much in agreement with you, until 
I got to your last paragraph. 

> 
> At the end of the day, this argument comes down to whether folks think
> that an RDMA mechanism is the right way to go and what RDMA scheme
> over IP is best. 

I agree. If you are transporting data between application memory and  
a remote periperal device, a scheme that permits direct DMA transfer
makes sense.  And, if we agree to that, it also makes sense to 
investigate a range of DMA transfer solutions, to see which provides 
the most appropriate capabilities, allows broad implementation, etc.

> A suitably generic RDMA scheme allows innovation in
> protocol design, without worrying that the new protocol will be
> hopelessly slow in legacy hardware.  It decreases the pressure to load
> features into old, hardware-supported protocols instead of introducing
> new ones. 

Here's where I must ask for a clarification. Are you saying that 
performance, or for that matter the ability to implement these 
solutions on existing hardware, is a "don't care"?  Or, are you
saying that a RDMA scheme is inherently efficient enough that
even legacy hardware will work just fine? 

I hope you meant the latter, but admit that my first 
impression was that you'd give up "legacy hardware" support 
for a fast protocol that could only run in a new hardware 
environment.

> It destroy an artificial barrier (host overhead) that
> prevents IP from scaling to fit all our needs.
>

Allowing IP to be used across a wider range of solutions is 
a good thing. Removing the perception that IP stacks are 
"cycle hogs" is a good thing, too.

But, I suggest that its history of maintaining compatibility 
with older hardware and software implementations is also a 
pretty good selling point for TCP/IP, and one that shouldn't 
be lightly dismissed.  

	- milan


Milan J. Merhar,  Chief Engineer, Pirus Networks,  
43 Nagog Park, Acton MA 01720-3425
voice:  978-206-9124  email: milan@pirus.com