RE: Requirements specification

[Michael Krause <krause@cup.hp.com>]

At 10:58 AM 8/4/00 -0700, psarkar@almaden.ibm.com wrote:

>Two points:
>
>1.  The iSCSI presenters seem to imply that having 'n' connections through 
>the IP fabric will automatically give you 'n' (or close to 'n') times the 
>bandwidth if you round-robin your packets across the connections. This is 
>probably true only in the very ideal case and in the real world, the 
>situation is far less rosy to make such an assertion so confidently.

Not true that this has to be the ideal world - there are numerous 
applications that maintain high-bandwidth through multiple connections on 
the same path or across several paths.  Also, network routers often 
implement RED / WRED schemes which may only impact a subset of the sessions 
connections.


>2. Fault-tolerance currently is (and should be) layered above the SCSI 
>transport layer. There are enough solutions from several vendors in the 
>market which deal with this,
>so there is no use in reinventing the wheel.

Fault tolerance is a highest level of availability there are other levels 
that allow one to recover from a variety of failure types without requiring 
to implement to this level.  Most of these can be simply implemented below 
the iSCSI level.  Also, dynamic changes in the network composition can be 
dealt with without resorting to high-level changes to the 
applications.  The objective of improving the availability is to not be 
required to use this overly complex solutions but to create simple, 
low-implementation costs solutions that will benefit the majority of the 
customers.

>Based on the "Keep It Simple and Stupid" and "Optimize for the Common Case"
>principles,I would appeal to the iSCSI "design team" to forgo multiple 
>connections per
>session and use specialized solutions for remote mirroring and remote tape 
>backup (the apps that require multiple connections).

Multiple connections can be done using a KISS principle and more robust 
solutions can be built on top of this solution to expand the functional 
capabilities without requiring the architecture to be radically permuted in 
the process.

Mike