Re: ISCSI: Urgent pointer consensus

[Daniel Smith <dfsmith@almaden.ibm.com>]

Matt Wakeley wrote:
> 
> placed.  If you lose an iSCSI PDU header due to a lost TCP segment, you
> lose iSCSI PDU framing from then on (until the missing segment is
> received).  You then have to store the TCP data (received after the

Ah!  Now I am beginning to see how your implementation works.  In your view,
a write CDB for 128MB would have a sequence like...

send CDB PDU
rx R2T for 1MB          (rx=receive)
send 1MB
rx R2T for 1MB
send 1MB
...
rx status PDU

... whereas some of us imagine something like...

send CDB PDU
rx R2T for 128MB
send 128MB
rx status PDU

For short transactions (<1MB) the urgent doesn't help much because R2Ts will
cover the whole amount of data.

For long transactions (>1MB) there may be some benefit, although with all
those R2Ts flying about TCP may lose streaming metrics.  Hmm, I'll give it
more thought, but this still seems very specialized and closely tied in with
your (and others) implementation view.

Daniel Smith.
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