Re: single vs multiple channels for iSCSI commands

[meth@il.ibm.com]

Matt,

We have to distinguish between the cases when the target and initiator have
agreed to use RTT or have agreed to not use RTT. When using RTT, the target
will have prepared the buffers before issuing the RTT. If the target has
agreed to not use RTT, that means the target agrees to provide spare
buffers to store whatever data may arrive on any of its data channels
before the corresponding commands arrive. When the command arrives on the
control channel, the target will be informed over which channel the data is
being sent for that command, and the target will be able to match up the
corresponding data buffers (including the data buffers that arrived before
the command arrived). If the target is very limited in resources, then it
shouldn't agree to work without RTT. If for some reason the target agreed
to work without RTT and it runs out of buffers, we allow the target to
discard data from its early arrival buffers and request that data to be
resent later on via an RTT.

In any case, the initiator may send immediate data over the control channel
in the same packet with the command. This should only be used for small
amounts of data (say up to 8K).

- Kalman




Matt Wakeley <matt_wakeley@agilent.com> on 04/07/2000 09:47:41

Please respond to Matt Wakeley <matt_wakeley@agilent.com>

To:   ips@ece.cmu.edu, scsi-tcp@external.cisco.com
cc:    (bcc: Kalman Meth/Haifa/IBM)
Subject:  Re: single vs multiple  channels for iSCSI commands




meth@il.ibm.com wrote:

> Proposal to support single Control Channel with multiple Data  Channels
> in the iSCSI protocol.

How would the requirement to send immediate data with commands be
supported?
(This would be Randy H's requirement to send write data without a RTT).  We
already agreed that immediate write data would be part of the command
message.  This would mean that all immediate write commands (with immediate
data) would be over the same channel.  So, then how would the striping
across
multiple channels be utilized? Oh, well send the data on another channel
you
say - ok, but what happens when the data arrives before the command?