Re: a vote for asymmetric connections in a session

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

Joshua Tseng wrote:

> John,
>
> "A lot of data" is relative.  The fastest TCP implementations available
> today
> don't come close to what will be required for iSCSI, since they peak out
> at about 200Mbps.  And the vast majority of applications are get much worse
> performance than that out of TCP--I would guess typically about 20Mbps max.
>
> iSCSI will use TCP like never before.  I believe FCP has flow control/
> command recovery mechanisms below SCSI.

Nope. FCP does not have *any* flow control mechanisms (Fibre Channel itself
does, but *not* the FCP protocol).
In addition, FCP does *not* have any command recovery mechisms either.  It uses
the "if the command doesn't complete within x amount of time, blow it away and
try again" recovery mechanism.

FCP-2 (which is still under developement, and not deployed) is attempting to
"recover" lost commands and data frames.  And this "recovery" is only meant for
devices such as tapes, and not discs.

-Matt


> Unlike iSCSI, FCP has the benefit of operating in a low latency environment
> (<10us).  To think iSCSI can do
> without it and still be able to function reliably is, well iffy at best from
> what I can see.
>
> Regads,
>
> Josh