Re: iSCSI: Session Partial Resolution

["Matt Wakeley" <matt_wakeley@agilent.com>]

Douglas Otis wrote:

> Matt,
>
>
> > The "iSCSI Requirements" document requires this capability:
> >
> > "[R] High bandwidth, bandwidth aggregation.
>
> This is a general feature of IP.

No, it's not.  Please go back and read Randy Haagens' memo from August 5,
available here
 http://ips.pdl.cs.cmu.edu/mail/msg00412.html

>
>
> > [D] The bandwidth (transfer rate, MB/sec) supported by storage
> > controllers is rapidly increasing, due to several factors: (1)
> > Increase in disk spindle and controller performance;
>
> The linear increase in the performance of the mechanical aspects of the
> drive have not kept pace with the exponential data density improvements.
> Unless dealing with a single massive transfer, the overall effect of data
> density improvements is a small reduction in latency lost by the large
> latency within a MAN network.

We are not talking about drive controllers, we're talking about storage array
(raid) controllers, where there is lots of drives behind it.

I don't think anyone considers attaching individual disk drives to the internet
(we'd very quickly run out of IP addresses).

>
>
> > (2) Use
> > of ever-larger caches, and improved caching algorithms;
>
> Network latency negates use of remote caching.  Such caching must be near
> the client and not the drive.  If you wish to define a controller
> specification, this should be done using appropriate technologies.  Clearly,
> if the controller is on site, interface requirements change substantially.
> For redundancy, there may even be one per client system! Now the traffic
> that needs some work would be to ensure such controllers stay synchronized
> if used in a cluster.  Either way, you will not see a higher performance
> moving the controller next to the drive.
>
> > (3)
> > Increased scale of storage controllers (number of supported
> > spindles, speed of interconnects). Not only must the iSCSI
> > provide for full utilization of available link bandwidth, it
> > also must exploit parallelism (multiple connections) at the
> > device interfaces and within the interconnect fabric."
>
> Again, this is a general feature of IP.  If access is to the drive, as it
> should be, there is no problem scaling especially if you are using IP.
>
> > Unless there is "consensus" that this is not required, I think
> > the multiple
> > connections/session must remain.
>
> Not one reason for forcing aggregation into a single connection.  If you
> wish to bind multiple adapters, IP supports this.  I doubt you will ever
> need to do this however.

I'm not going to try and convince you of the need for iSCSI link aggregation,
and how IP does not support this.  Bottom line is that major system and storage
vendors such as HP think we need it.  Once again, re-read Randy's message.

>
>
> Doug

-Matt