Re: multiple connections

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

somesh_gupta@hp.com wrote:

> > -----Original Message-----
> > From: rsnively@Brocade.COM [mailto:rsnively@Brocade.COM]

<snip>

> > And to top it off, the target is active with a large number of
> > initiators on behalf of a large number of logical units for a large
> > number of queued commands, so there is absolutely no guarantee that
> > any buffer exists for the data that was received, even if the
> > command had been received first.
> >
> > Every SCSI command execution is managed by the target for
> > this reason among
> > many others.  Thus RTT has been a part of every SCSI protocol
> > for write
> > operations.
> >
>
> TCP window size should provide a reasonable flow control mechanism,
> so an additional flow control should not be needed. There will be
> some statistical determination of the amount of memory needed in
> a large array vs the window size extended on each connection.
>
> I don't know if arrays like to keep commands in seperate memory
> from data, in which case a command queue depth may have to be
> communicated seperately (assuming most of window would typically
> be used for data)

Arrays very much do like to keep commands in separate memory from data.  In
fact, they like the data for a particular I/O to go to a particular place in
memory.  And they don't want that data arriving before they have this
particular place set up and ready for it.  That's why (most) arrays implement
the RTT.  It is not for flow control, it is for array memory management.

(the array vendors can flame me for being way off base)

-Matt Wakeley
Agilent Technologies